rds: ib: Fix uninitialized variable

send_flags needs to be initialized before calling
rds_ib_set_wr_signal_state().

Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>