Grey out wifi tethering in airplane mode

When airplane mode is enabled, wifi tethering
should be disabled since there is no real
use case for it.

This also addresses the issue
of trying to restore Wifi (with tethering on)
when airplane mode is disabled.

Bug: 2594720
Change-Id: I7379ebed74a58b148ae82ed589d09aa2b9ca767d
1 file changed