Add a compile time check that the buffer that we allocate on the stack
is reasonably small.

NM_UTILS_LOOKUP_STR() uses alloca(). Partly to avoid the overhead of
malloc(), but more important because it's convenient to use. It does
not require to declare a varible to manage the lifetime of the heap
allocation.

It's quite safe, because the stack allocation is of a fixed size of only
a few bytes. Overall, I think the convenience that we get (resulting in
simpler code) outweighs the danger of stack allocation in this case. It's
still worth it.
However, as it uses alloca(), it still must not be used inside a (unbound)
loop and it is obviously a macro.

Rename the macros to have a _A() suffix. This should make the
peculiarities more apparent.

The only purpose of using alloca() to avoid the overhead of heap-allocation
and possible save a line in source code for managing/freeing the heap allocation.

For tests we don't care about performance, and (in this case)
the code does not get any shorter.

Avoid alloca() in tests, because alloca() is something to search for
when reviewing code for stack overflows. No need to have such false
positives show up in tests.

https://bugzilla.redhat.com/show_bug.cgi?id=1665649

 nmcli connection modify t ipv4.dns-options ndots:2
 nmcli connection modify t +ipv4.dns-options ndots:4

should set dns-options to 'ndots:4', so we must remove other
occurences of the same option before adding it, otherwise the setting
refuses to set the same option again.

Appending to the ipvx.dns-options property:

  nmcli connection modify con +ipv4.dns-options rotate

currently is buggy because it resets the list to contain only
'rotate'. The setter function should not clear the list.

https://bugzilla.redhat.com/show_bug.cgi?id=1665649

wpa_supplicant is going to change the global default for PMF from 0
(disabled) to 1 (optional) [1], so NM code needs to be adjusted to
work with all wpa_supplicant versions. Furthermore, it is better to
set optional PMF using the 'Pmf' property instead of the 'ieee80211w'
configuration option because the former better handles missing support
in driver [2].

Note that each interface in wpa_supplicant has its own copy of global
configuration and so 'global' options must still be set on each
interface. So, let's set Pmf=1 when each interface gets created and
override it with ieee80211w={0,2} if needed during association.

[1] http://lists.infradead.org/pipermail/hostap/2018-November/039009.html
[2] http://lists.infradead.org/pipermail/hostap/2019-January/039215.html

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/104

https://github.com/NetworkManager/NetworkManager/pull/277