mac80211: fix memory corruption in EAPOL handling

Commit e3d40304 ("mac80211: do not accept/forward invalid EAPOL
frames") uses skb_mac_header() before eth_type_trans() is called
leading to incorrect pointer, the pointer gets written to. This issue
has appeared during backporting to 4.4, 4.9 and 4.14.

Fixes: e3d40304 ("mac80211: do not accept/forward invalid EAPOL frames")
Link: https://lore.kernel.org/r/CAHQn7pKcyC_jYmGyTcPCdk9xxATwW5QPNph=bsZV8d-HPwNsyA@mail.gmail.com


Cc: <stable@vger.kernel.org> # 4.4.x
Signed-off-by: Davis Mosenkovs <davis@mosenkovs.lv>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>