x/net/icmp: fix typos in comments

Change-Id: I43ad7497db6b4d57efd2ab94f7af26e3eb0dcdf5
Reviewed-on: https://go-review.googlesource.com/18485
Reviewed-by: Ian Lance Taylor <iant@golang.org>

icmp/extension.go

@@ -10,7 +10,7 @@ type Extension interface {
 	// Proto must be either the ICMPv4 or ICMPv6 protocol number.
 	Len(proto int) int
 
-	// Marshal returns the binary enconding of ICMP extension.
+	// Marshal returns the binary encoding of ICMP extension.
 	// Proto must be either the ICMPv4 or ICMPv6 protocol number.
 	Marshal(proto int) ([]byte, error)
 }

icmp/message.go

@@ -59,7 +59,7 @@ type Message struct {
 	Body     MessageBody // body
 }
 
-// Marshal returns the binary enconding of the ICMP message m.
+// Marshal returns the binary encoding of the ICMP message m.
 //
 // For an ICMPv4 message, the returned message always contains the
 // calculated checksum field.

icmp/messagebody.go

@@ -10,7 +10,7 @@ type MessageBody interface {
 	// Proto must be either the ICMPv4 or ICMPv6 protocol number.
 	Len(proto int) int
 
-	// Marshal returns the binary enconding of ICMP message body.
+	// Marshal returns the binary encoding of ICMP message body.
 	// Proto must be either the ICMPv4 or ICMPv6 protocol number.
 	Marshal(proto int) ([]byte, error)
 }