net/rds: Initialize ic->i_fastreg_wrs upon allocation

Otherwise, if an IB connection is torn down before "rds_ib_setup_qp"
is called, the value of "ic->i_fastreg_wrs" is still at zero
(as it wasn't initialized by "rds_ib_setup_qp").
Consequently "rds_ib_conn_path_shutdown" will spin forever,
waiting for it to go back to "RDS_IB_DEFAULT_FR_WR",
which of course will never happen as there are no
outstanding work requests.

Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>