[wol] Make MAC regex case-insensitive

Change-Id: Ie1863cb1b13139bcc4f2ce826dc461bc4b993147
diff --git a/pdu/wol/wol.go b/pdu/wol/wol.go
index 3cc2fb4..1ec7777 100644
--- a/pdu/wol/wol.go
+++ b/pdu/wol/wol.go
@@ -12,7 +12,7 @@
 )
 
 var (
-	macAddrRegex = regexp.MustCompile(`^([0-9A-F]{2}[:-]){5}([0-9A-F]{2})$`)
+	macAddrRegex = regexp.MustCompile(`(?i)^([0-9A-F]{2}[:-]){5}([0-9A-F]{2})$`)
 	// Magic Packet header is 0xFF repeated 6 times.
 	magicPacketHeader = []byte{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}
 )