lib: Add back sockunion_str2su

* sockunion.h: Add back sockunion_str2su, its removal breaks things needlessly
  (e.g. our own unit tests).
* sockunion.c: (sockunion_str2su) implement on top of str2sockunion.
diff --git a/lib/sockunion.c b/lib/sockunion.c
index 37dc3f9..5dcf725 100644
--- a/lib/sockunion.c
+++ b/lib/sockunion.c
@@ -174,6 +174,18 @@
   return NULL;
 }
 
+union sockunion *
+sockunion_str2su (const char *str)
+{
+  union sockunion *su = XCALLOC (MTYPE_SOCKUNION, sizeof (union sockunion));
+  
+  if (!str2sockunion (str, su))
+    return su;
+  
+  XFREE (MTYPE_SOCKUNION, su);
+  return NULL;
+}
+
 /* Convert IPv4 compatible IPv6 address to IPv4 address. */
 static void
 sockunion_normalise_mapped (union sockunion *su)
diff --git a/lib/sockunion.h b/lib/sockunion.h
index 1a0a3c9..b9f3514 100644
--- a/lib/sockunion.h
+++ b/lib/sockunion.h
@@ -88,6 +88,7 @@
 extern int sockunion_cmp (union sockunion *, union sockunion *);
 extern int sockunion_same (union sockunion *, union sockunion *);
 
+extern union sockunion *sockunion_str2su (const char *str);
 extern int sockunion_accept (int sock, union sockunion *);
 extern int sockunion_stream_socket (union sockunion *);
 extern int sockopt_reuseaddr (int);