Add a new device state reason code for unsupported IP method. It is
returned, for example, when users select manual IP configuration for
WWAN connections:

 # nmcli connection mod Gsm ipv4.method manual ipv4.address 1.2.3.4/32
 # nmcli connection up Gsm
 Error: Connection activation failed: The selected IP method is not
 supported

compared to the old:

 Error: Connection activation failed: IP configuration could not be
 reserved (no available address, timeout, etc.)

Note that we could instead fail the connection validation if the
method is not supported by the connection type, but adding such
limitation now could make existing connections invalid.

https://bugzilla.redhat.com/show_bug.cgi?id=1459529