[review] dcbw/carrier-fixes: fix carrier handling for master devices and IPv4 method matching (bgo #725261)

[Dan Williams <dcbw redhat com>]

Recently we broke carrier handling during IP setup for master devices
when ignore-carrier is set, such that DHCP would be attempted even if
the device had no carrier, which is guaranteed to fail.  Only static
configuration should be allowed to proceed when the master has no
carrier.

Second, if DHCP or IPv4 addressing fails (due to the above problem) and
thus the interface has no IPv4 address, and NetworkManager is restarted,
the generated connection would read the IPv4 method as "disabled"
because the interface had no IPv4 addresses.  This caused match failures
to existing connections where the IPv4 method was 'auto', which was in
fact the pre-restart method.  So if the interface has no carrier, allow
matching between IPv4 disabled and auto methods.

https://bugzilla.gnome.org/show_bug.cgi?id=725261