staging/lustre/o2iblnd: connection refcount fix for kiblnd_post_rx
kiblnd_post_rx() can't refer to rx::rx_conn anymore after
ib_post_recv() because this rx can be polled out by another thread
which may drop this rx and destroy rx::rx_conn.
This patch fixes this issue by taking an extra refcount on connection
before calling ib_post_recv().