cfg80211: correct bridge/4addr mode check

Without the patch we fail:

$ sudo brctl addbr br0
$ sudo brctl addif br0 wlp1s0
$ sudo iw wlp1s0 set 4addr on
command failed: Device or resource busy (-16)

Last command failed but iface was already in 4addr mode.

Fixes: ad4bb6f8 ("cfg80211: disallow bridging managed/adhoc interfaces")
Signed-off-by: Janusz Dziedzic <janusz.dziedzic@gmail.com>
Link: https://lore.kernel.org/r/20211024201546.614379-1-janusz.dziedzic@gmail.com


[add fixes tag, fix indentation, edit commit log]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>