Fix endianness handling of srq_limit: it is big-endian in the context
structure, so we need to swab it before returning it.

Also add support for srq_limit query for Tavor (non-MemFree) HCAs.
Signed-off-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>