patch 8.2.0557: no IPv6 support for channels

Problem:    No IPv6 support for channels.
Solution:   Add IPv6 support. (Ozaki Kiichi, closes #5893)
diff --git a/src/version.c b/src/version.c
index 7095794..f1e274b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    557,
+/**/
     556,
 /**/
     555,