libibverbs: Introduce XRC domains

XRC introduces several new concepts and structures, one of
which is the XRC domain.

XRC domains: xrcd's are a type of protection domain used to
associate shared receive queues with xrc queue pairs.  Since
xrcd are meant to be shared among multiple processes, we
introduce new APIs to open/close xrcd's.

The user to kernel ABI is extended to account for opening/
closing the xrcd.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>