smb: client: allocate enough space for MR WRs and ib_drain_qp()

The IB_WR_REG_MR and IB_WR_LOCAL_INV operations for smbdirect_mr_io
structures should never fail because the submission or completion queues
are too small. So we allocate more send_wr depending on the (local) max
number of MRs.

While there also add additional space for ib_drain_qp().

This should make sure ib_post_send() will never fail
because the submission queue is full.

Fixes: f198186a ("CIFS: SMBD: Establish SMB Direct connection")
Fixes: cc55f65d ("smb: client: make use of common smbdirect_socket_parameters")
Cc: stable@vger.kernel.org
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>