RDMA/cxgb4: Configure 0B MRs to match HW implementation

0B MRs need some tweaks to work correctly with HW. When writing the
TPTE, if the MR length is zero we now:

1) turn off all permissions
2) set the length to -1

While functionality/capabilities of the MR are the same with these
changes, it resolves a dapltest 0B RDMA Read test failure.  Based on
original work by Steve Wise <swise@opengridcomputing.com>.

Signed-off-by: Pramod Kumar <pramod@chelsio.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/cxgb4/mem.c

@@ -369,9 +369,11 @@ static int register_mem(struct c4iw_dev *rhp, struct c4iw_pd *php,
 	int ret;
 
 	ret = write_tpt_entry(&rhp->rdev, 0, &stag, 1, mhp->attr.pdid,
-			      FW_RI_STAG_NSMR, mhp->attr.perms,
+			      FW_RI_STAG_NSMR, mhp->attr.len ?
+			      mhp->attr.perms : 0,
 			      mhp->attr.mw_bind_enable, mhp->attr.zbva,
-			      mhp->attr.va_fbo, mhp->attr.len, shift - 12,
+			      mhp->attr.va_fbo, mhp->attr.len ?
+			      mhp->attr.len : -1, shift - 12,
 			      mhp->attr.pbl_size, mhp->attr.pbl_addr);
 	if (ret)
 		return ret;