mac80211: make mgmt_tx accept a NULL channel
mac80211: make mgmt_tx accept a NULL channel

cfg80211 passes a NULL channel to mgmt_tx if the frame has
to be sent on the one currently in use by the device.
Make the implementation of mgmt_tx correctly handle this
case. Fail if offchan is required.

Signed-off-by: Antonio Quartulli <a08f08bac39aeae6c9580ade7aa8387b5a0e7428@open-mesh.com>
[fix RCU locking]
Signed-off-by: Johannes Berg <bff32994ff0f8d048f262a8388145a71b6071bfe@intel.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs