internal/socket: use larger buffers in race test

The race detector doesn't seem to track races at the byte level.
Use a larger buffer to make the test more reliable.

Fixes golang/go#37338

Change-Id: I275db68a5c206b58c3bc48b9f5c1e22ee1aff176
Reviewed-on: https://go-review.googlesource.com/c/net/+/312529
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

internal/socket/socket_test.go

@@ -325,8 +325,8 @@ func main() {
 	}
 	cc := ipv4.NewPacketConn(c)
 	sync := make(chan bool)
-	src := make([]byte, 1)
-	dst := make([]byte, 1)
+	src := make([]byte, 100)
+	dst := make([]byte, 100)
 	go func() {
 		if _, err := cc.WriteTo(src, nil, c.LocalAddr()); err != nil {
 			log.Fatalf("WriteTo: %v", err)
@@ -358,8 +358,8 @@ func main() {
 	}
 	cc := ipv4.NewPacketConn(c)
 	sync := make(chan bool)
-	src := make([]byte, 1)
-	dst := make([]byte, 1)
+	src := make([]byte, 100)
+	dst := make([]byte, 100)
 	go func() {
 		if _, err := cc.WriteTo(src, nil, c.LocalAddr()); err != nil {
 			log.Fatalf("WriteTo: %v", err)