net/stun: convert to use net/netip.AddrPort

Convert ParseResponse and Response to use netip.AddrPort instead of
net.IP and separate port.

Fixes #5281

Signed-off-by: Kris Brandow <kris.brandow@gmail.com>

net/stun/stun_fuzzer.go

@@ -7,7 +7,7 @@
 package stun
 
 func FuzzStunParser(data []byte) int {
-	_, _, _, _ = ParseResponse(data)
+	_, _, _ = ParseResponse(data)
 
 	_, _ = ParseBindingRequest(data)
 	return 1