IB/iser: Don't change itt endianness

The itt field in struct iscsi_data is not defined with any particular
endianness.  open-iscsi should use it as-is without byte-swapping it.
This fixes sparse warnings coming from doing ntohl(hdr->itt).

Signed-off-by: Erez Zilber <erezz@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>