If the Windows Sniffer writes out one of its ATM capture files in DOS

If the Windows Sniffer writes out one of its ATM capture files in DOS
Sniffer format, it doesn't distinguish between LE Control and LANE
encapsulated LAN frames, so we can't rely on the ATM subtype being
correct even when reading DOS Sniffer captures - we force it to
TRAF_ST_LANE_LE_CTRL for LANE frames that begin with 0xff 0x00.

Move the calls to "infer_pkt_encap()" into "fix_pseudo_header()".

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@6869 f5534014-38df-0310-8fa8-9805f1628bb7