mwifiex: fix an issue with Appletalk devices

SNAP/LLC header in the AARP packet is being stripped off while
preparing an EthernetII header.
Annex M, Table M.3 in 802.11 spec says that some header
(ex. AppleTalk AARP(2)) should pass through untouched.
This patch modifies the check to exclude/include EthernetII
header translation for special cases.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>