mac80211: detect existing interface before adding

mac80211: detect existing interface before adding

Keep existing wdev when creating new nl80211 interfaces if phy and
type match, delete it otherwise.
To make this work, also remove left-over debugging function which
prevented the return-value of the 'iw' command to be taken into
account in mac80211_iw_interface_add().
As 4addr-mode (WDS) was setup during interface creation for station
interfaces, also set it after interface creation to make sure an
existing sta interface ends up with the right mode.

Fixes: a5bc9787d4 ("mac80211: add support for dynamically
                    reconfiguring wifi")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>