RDS: introduce rds_conn_connect_if_down()

A few paths had the same block of code to queue a connection's connect work if
it was in the right state.  Let's move this in to a helper function.

Signed-off-by: Zach Brown <zach.brown@oracle.com>
diff --git a/net/rds/rds.h b/net/rds/rds.h
index 4ab3d1a..cba5f8b 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -617,6 +617,7 @@
 void rds_conn_destroy(struct rds_connection *conn);
 void rds_conn_reset(struct rds_connection *conn);
 void rds_conn_drop(struct rds_connection *conn);
+void rds_conn_connect_if_down(struct rds_connection *conn);
 void rds_for_each_conn_info(struct socket *sock, unsigned int len,
 			  struct rds_info_iterator *iter,
 			  struct rds_info_lengths *lens,