ipv6: fix typo in package documentation

Change-Id: I94a8b7e876a8cbe4d565bab021f16c1c91f5aa10
Reviewed-on: https://go-review.googlesource.com/12651
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

ipv6/doc.go

@@ -114,7 +114,7 @@
 //			// error handling
 //		}
 //		if rcm.Dst.IsMulticast() {
-//			if rcm.Dst.Equal(group)
+//			if rcm.Dst.Equal(group) {
 //				// joined group, do something
 //			} else {
 //				// unknown group, discard