brcmfmac: fix lockup when removing P2P interface after event timeout

Removing P2P interface is handled by sending a proper request to the
firmware. On success firmware triggers an event and driver's handler
removes a matching interface.

However on event timeout we remove interface directly from the cfg80211
callback. Current code doesn't handle this case correctly as it always
assumes rtnl to be unlocked.

Fix it by adding an extra rtnl_locked parameter to functions and calling
unregister_netdevice when needed.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>