doc: mention net.SocketConn, net.SocketPacketConn in go1.5.txt

Change-Id: I6bda19877ae5148ad349cfb8929f1103740422bb
Reviewed-on: https://go-review.googlesource.com/10005
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: cixtor

doc/go1.5.txt

@@ -53,6 +53,7 @@ mime: add ExtensionByType (https://golang.org/cl/7444)
 mime/quotedprintable: new package (https://golang.org/cl/5940 + others)
 net: add Source field to OpError (https://go-review.googlesource.com/9231)
 net: fix inconsistent errors (https://golang.org/cl/9236)
+net: add SocketConn, SocketPacketConn (https://golang.org/cl/9275)
 net/http: support for setting trailers from a server Handler (https://golang.org/cl/2157)
 net/http: ignore the Unix epoch time in ServeContent (https://golang.org/cl/7915)
 net/http/cgi: fix REMOTE_ADDR, REMOTE_HOST, add REMOTE_PORT (https://golang.org/cl/4933)