LU-3164 utils: Fix Wireshark decode of Lustre under Infiniband

LU-3164 utils: Fix Wireshark decode of Lustre under Infiniband

Due to a difference in the IB LND vs TCP LND header sizes, some
hard-coded offsets in the LNet dissector will not believe that the
payload is lustre.  As such, the lustre protocol may not be decoded
under Infiniband.

This patch addresses this by adding a variable to applicable offsets
which is set to 0 for TCP, and 24 (extra bytes in IB LND header)
for Infiniband.

Signed-off-by: Doug Oucharek <doug.s.oucharek@intel.com>
Change-Id: I3783bbb563df109e160752d246db9bc5148cf132
Reviewed-on: http://review.whamcloud.com/6045
Tested-by: Hudson
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Amir Shehata <amir.shehata@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>