net: update DialIP comments to mention protocols

Fixes #2637.

R=golang-dev, mikioh.mikioh, iant
CC=golang-dev
https://golang.org/cl/5508043

src/pkg/net/iprawsock_plan9.go

@@ -84,8 +84,8 @@ func splitNetProto(netProto string) (net string, proto int, err error) {
 	return
 }
 
-// DialIP connects to the remote address raddr on the network net,
-// which must be "ip", "ip4", or "ip6".
+// DialIP connects to the remote address raddr on the network protocol netProto,
+// which must be "ip", "ip4", or "ip6" followed by a colon and a protocol number or name.
 func DialIP(netProto string, laddr, raddr *IPAddr) (c *IPConn, err error) {
 	return nil, os.EPLAN9
 }

src/pkg/net/iprawsock_posix.go

@@ -224,8 +224,8 @@ func splitNetProto(netProto string) (net string, proto int, err error) {
 	return net, proto, nil
 }
 
-// DialIP connects to the remote address raddr on the network net,
-// which must be "ip", "ip4", or "ip6".
+// DialIP connects to the remote address raddr on the network protocol netProto,
+// which must be "ip", "ip4", or "ip6" followed by a colon and a protocol number or name.
 func DialIP(netProto string, laddr, raddr *IPAddr) (c *IPConn, err error) {
 	net, proto, err := splitNetProto(netProto)
 	if err != nil {