ipv4: fix typo in comment

Change-Id: I60db66b5bbe25b434d8ec1fbc031438a16720dfa
GitHub-Last-Rev: 152f0ce49bf929a7859818f19c8f76da9c844e27
GitHub-Pull-Request: golang/net#30
Reviewed-on: https://go-review.googlesource.com/c/163865
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

ipv4/doc.go

@@ -209,7 +209,7 @@
 // LeaveSourceSpecificGroup for the operation known as "include" mode,
 //
 //	ssmgroup := net.UDPAddr{IP: net.IPv4(232, 7, 8, 9)}
-//	ssmsource := net.UDPAddr{IP: net.IPv4(192, 168, 0, 1)})
+//	ssmsource := net.UDPAddr{IP: net.IPv4(192, 168, 0, 1)}
 //	if err := p.JoinSourceSpecificGroup(en0, &ssmgroup, &ssmsource); err != nil {
 //		// error handling
 //	}