mac80211: allow self-protected frame tx without sta

Useful for userspace mesh to authenticate and peer without
a station entry, since both steps may fail anyway.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
mac80211: initialize nonpeer_pm

XXX: hack! but the context changed upstream anyway, don't
submit from this branch!

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>