mac820154: move mutex locks out of loop

Instead of always re-lock the iflist_mtx at multiple interfaces we lock
the complete for each loop at start and at the end.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

diff --cc net/mac802154/iface.c
Simple merge