mac80211: fix header ops

When using recvfrom() on a SOCK_DGRAM packet socket, I noticed that the MAC
address passed back for wireless frames was always completely wrong. The
reason for this is that the header parse function assigned to our virtual
interfaces is a function parsing an 802.11 rather than 802.3 header. This
patch fixes it by keeping the default ethernet header operations assigned.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>