nl80211: Ignore 4addr mode enabling error if it was already enabled

nl80211: Ignore 4addr mode enabling error if it was already enabled

nl80211_set_4addr_mode() could fail when trying to enable 4addr mode on
an interface that is in a bridge and has 4addr mode already enabled.
This operation would not have been necessary in the first place and this
failure results in disconnecting, e.g., when roaming from one backhaul
BSS to another BSS with Multi AP.

Avoid this issue by ignoring the nl80211 command failure in the case
where 4addr mode is being enabled while it has already been enabled.

Signed-off-by: Jouni Malinen <j@w1.fi>