There are a few cases where we don't want to clear a potential
nm-generated/volatile flag, but only mark the connection as
unsaved.

Otherwise, we wrongly end up clearing these flags and the connection
is wrongly not NM_DEVICE_SYS_IFACE_STATE_EXTERNAL.

Fixes: 35dc6421de78cffd1761cfb6edf9e94233f99966

Format:

  QDISC1=ingress
  QDISC2="root handle 1234: fq_codel"
  FILTER1="parent ffff: matchall action simple sdata Input"
  FILTER2="parent 1234: matchall action simple sdata Output"

Perhaps a cargo cult leftover.

Fixes: c3dd5d8df2388813c22d2662985725b188450b85

DNS searches from the ipv4 and ipv6 settings were joined and written
to the same ifcfg-rh "DOMAIN" variable and so the connection read back
from disk was different from the one written.

Instead, introduce a separate variable for ipv6 searches; to preserve
backwards compatibility, still read the "DOMAIN" variable for ipv6
when ipv4 is disabled so that we don't lose DNS searches on upgrade.

https://bugzilla.redhat.com/show_bug.cgi?id=1517794

This is now required as we instance inotify-helper only on need:
we have to init them to the unset value, otherwise...

	Thread 1 "NetworkManager" received signal SIGSEGV, Segmentation fault.
	nm_inotify_helper_remove_watch (self=0x0, wd=0) at src/settings/plugins/ifcfg-rh/nm-inotify-helper.c:100
	100		if (priv->ifd < 0)
	(gdb) backtrace
	#0  0x00007fffe35da6c0 in nm_inotify_helper_remove_watch (self=0x0, wd=0) at src/settings/plugins/ifcfg-rh/nm-inotify-helper.c:100
	#1  0x00007fffe35d45b1 in nm_inotify_helper_clear_watch (wd=0x7fffdc008628, helper=<optimized out>) at src/settings/plugins/ifcfg-rh/nm-inotify-helper.h:53
	#2  0x00007fffe35d45b1 in path_watch_stop (self=0x7fffdc0085f0) at src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-connection.c:223
	#3  0x00007fffe35d467c in filename_changed (object=0x7fffdc0085f0, pspec=<optimized out>, user_data=<optimized out>) at src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-connection.c:242
	#4  0x00007ffff61b230d in g_closure_invoke () at /lib64/libgobject-2.0.so.0
	#5  0x00007ffff61c498e in signal_emit_unlocked_R () at /lib64/libgobject-2.0.so.0
	#6  0x00007ffff61cd1a5 in g_signal_emit_valist () at /lib64/libgobject-2.0.so.0
	#7  0x00007ffff61cdb0f in g_signal_emit () at /lib64/libgobject-2.0.so.0
	#8  0x00007ffff61b6594 in g_object_dispatch_properties_changed () at /lib64/libgobject-2.0.so.0
	#9  0x00007ffff61b5f3e in g_object_notify_queue_thaw () at /lib64/libgobject-2.0.so.0
	#10 0x00007ffff61b7776 in g_object_new_internal () at /lib64/libgobject-2.0.so.0
	#11 0x00007ffff61b924d in g_object_new_valist () at /lib64/libgobject-2.0.so.0
	#12 0x00007ffff61b9691 in g_object_new () at /lib64/libgobject-2.0.so.0
	#13 0x00007fffe35d5018 in nm_ifcfg_connection_new (source=source@entry=0x0, full_path=full_path@entry=0x555555a9a590 "/etc/sysconfig/network-scripts/ifcfg-team3", error=error@entry=0x7fffffffdc30, out_ignore_error=out_ignore_error@entry=0x7fffffffdc2c) at src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-connection.c:429
	#14 0x00007fffe35d5e96 in update_connection (self=self@entry=0x555555a59ea0, source=source@entry=0x0, full_path=0x555555a9a590 "/etc/sysconfig/network-scripts/ifcfg-team3", connection=connection@entry=0x0, protect_existing_connection=protect_existing_connection@entry=0, protected_connections=protected_connections@entry=Python Exception <class 'gdb.error'> There is no member named keys.:
	0x555555a9fc00, error=0x0) at src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-plugin.c:218
	#15 0x00007fffe35d7073 in read_connections (plugin=plugin@entry=0x555555a59ea0) at src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-plugin.c:545
	#16 0x00007fffe35d72f1 in get_connections (config=0x555555a59ea0) at src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-plugin.c:581
	#17 0x00005555556bb513 in load_connections (self=0x555555a1a920) at src/settings/nm-settings.c:239
	#18 0x00005555556bb513 in nm_settings_start (self=0x555555a1a920, error=<optimized out>) at src/settings/nm-settings.c:1800
	#19 0x00005555555ada1f in nm_manager_start (self=0x555555a490c0, error=<optimized out>) at src/nm-manager.c:5262
	#20 0x00005555555851ae in main (argc=<optimized out>, argv=<optimized out>) at src/main.c:417

Fixes: 31f2a466390024be6710b259d5ad228ebf5d1557