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>

net/rds/af_rds.c

@@ -40,6 +40,15 @@
 
 #include "rds.h"
 
+char *rds_str_array(char **array, size_t elements, size_t index)
+{
+	if ((index < elements) && array[index])
+		return array[index];
+	else
+		return "unknown";
+}
+EXPORT_SYMBOL(rds_str_array);
+
 /* this is just used for stats gathering :/ */
 static DEFINE_SPINLOCK(rds_sock_lock);
 static unsigned long rds_sock_count;