rdma: api: prepare support for direct verb

rdma: api: prepare support for direct verb

Prepare rdma interface creation API for direct verb support:
 - add new optional 'mode' parameters to select between ibverb or direct
   verb backend (optional, default to 'auto')
 - set default value for rxq_num (1), rxq_size (1024) and txq_size
   (1024) so they are now optional
 - bump default create value for rxq_size and txq_size to 1024 if
   unset (0) so they are coherent with default values above

Type: feature

Change-Id: Id9eae2b8eb0baaf34a0fcd55da6ad09515f57a93
Signed-off-by: Benoît Ganne <bganne@cisco.com>