RDS/IB: print string constants in more places

This prints the constant identifier for work completion status and rdma
cm event types, like we already do for IB event types.

A core string array helper is added that each string type uses.

Signed-off-by: Zach Brown <zach.brown@oracle.com>
diff --git a/net/rds/ib.h b/net/rds/ib.h
index 2189fd4..7ad3d57 100644
--- a/net/rds/ib.h
+++ b/net/rds/ib.h
@@ -345,6 +345,7 @@
 extern wait_queue_head_t rds_ib_ring_empty_wait;
 
 /* ib_send.c */
+char *rds_ib_wc_status_str(enum ib_wc_status status);
 void rds_ib_xmit_complete(struct rds_connection *conn);
 int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 		unsigned int hdr_off, unsigned int sg, unsigned int off);