xprtrdma: Disable completions for FAST_REG_MR Work Requests

Instead of relying on a completion to change the state of an FRMR
to FRMR_IS_VALID, set it in advance. If an error occurs, a completion
will fire anyway and mark the FRMR FRMR_IS_STALE.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Tested-by: Shirley Ma <shirley.ma@oracle.com>
Tested-by: Devesh Sharma <devesh.sharma@emulex.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>