Handle big-endian Prism headers.

Apparently, some systems write out big-endian Prism headers (probably
big-endian-MIPS-based Wi-Fi APs running $LINUX_DISTRIBUTION and the
like), so check for both big-endian and little-endian message codes,
and, for the fields in the header, use the byte order that matched.

Change-Id: Ia13df606676bb7dbc5d12fe4e297681bebb6f478
Reviewed-on: https://code.wireshark.org/review/759
Reviewed-by: Guy Harris <guy@alum.mit.edu>
Reviewed-on: https://code.wireshark.org/review/761
[Automatic manuf, services and enterprise-numbers update for 2014-03-23]

Change-Id: Ica2416485fc7aa0b2b703c3b695f527e6f966e59
Reviewed-on: https://code.wireshark.org/review/795
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>