rtlwifi: Fix endian error in extracting packet type

All of the rtlwifi drivers have an error in the routine that tests if
the data is "special". If it is, the subsequant transmission will be
at the lowest rate to enhance reliability. The 16-bit quantity is
big-endian, but was being extracted in native CPU mode. One of the
effects of this bug is to inhibit association under some conditions
as the TX rate is too high.

Based on suggestions by Joe Perches, the entire routine is rewritten.

One of the local headers contained duplicates of some of the ETH_P_XXX
definitions. These are deleted.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: Stable <stable@vger.kernel.org> [2.6.38+]
Signed-off-by: John W. Linville <linville@tuxdriver.com>