musl libc does not implement the canonicalize_file_name() GNU extension.
Use the POSIX standard realpath() instead.

GVfs' libgvfsdbus.so GIo module, when automatically loaded, attempts to
discover if there's a session D-Bus instance to use. It tries real hard
to get the socket name it would use -- in absence of XDG_RUNTIME_DIR it
decides to make it up with user's home directory. When HOME is unset
too, it just tries to figure it out by looking into /etc/passwd. Which
upsets SELinux that would better not see us looking into it.

We trigger the load of the GIo modules, by using the GFile API to access
the the ports in /dev. They're utterly uesless to us, but there doesn't
seem to be a way to disable their load. Oh well.

For now, let's just ensure HOME is set and the problematic path in glib
is not taken.

The mm_call_list_add_call() takes a full reference to the call, so we
can unref the original one safely.

They were reversed; ringing in applies to incoming calls, ringing out
applies to outgoing calls.

Commit 2a97e39cdd in libmim ("libmbim-glib: add additional cause codes
to MbimNwError") added additional cause codes to MbimNwError. This
patch maps some of those MbimNwError to MMMobileEquipmentError.

This patch requires libmbim >= 1.17.1

assure_qmi_client() was created to help migrating MMBroadbandModemQmi code
to use GTask. Now that all MMBroadbandModemQmi code has been migrated to
use GTask, this patch removes the old ensure_qmi_client() and rename
assure_qmi_client() as ensure_qmi_client().