wifi: Use SSID from connection also if AP is not configured

Creating a mode=ap connection (as GNOME control center does) would otherwise
assert in complete_connection despite having a proper SSID set:

NetworkManager-wifi:ERROR:nm-device-wifi.c:1118:complete_connection: assertion failed: (ssid)
Aborted
cli: Add mode option for wifi connecitons

Only default (infrastructure) mode connections can be created and as it's not
possible to write mode=ap connections with ifcfg-rh plugins, they can't be
switched to mode=ap.
ifcfg-rh: add support for MODE=Ap

It is an extension against initscripts. However, we have many other Wi-Fi
related extensions. So the NM-written ifcfg file will not be 100% backwards
compatible anyway.
Moreover, initscripts changed from using iwconfig to iw and dropped support
(accidently?) for some traditional variable, like KEY1-KEY4, CHANNEL, etc.
They should be fixed bring back by initscripts.
https://git.fedorahosted.org/cgit/initscripts.git/commit/sysconfig/network-scripts/ifup-wireless?id=ddda5f6f818831b1fa37337be0ac9c0f619df1ca
Merge branch 'lr/ap'

https://bugzilla.gnome.org/show_bug.cgi?id=738439