carl9170: allow P2P_GO interface creation after P2P_CLIENT

Janusz Dziedzic reported that after a change in wpa_supplicant
["nl80211: Automatically use concurrent P2P if possible"],
carl9170 was no longer able to host a P2P network.

This patch tackles the problem by allowing GO interfaces to be
registered, long after the P2P_CLIENT interface is brought up.

Reported-by: Janusz Dziedzic <janusz.dziedzic@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>