p2p: add 0 port check in dialer (#21008)

* p2p: add low port check in dialer

We already have a check like this for UDP ports, add a similar one in
the dialer. This prevents dials to port zero and it's also an extra
layer of protection against spamming HTTP servers.

* p2p/discover: use errLowPort in v4 code

* p2p: change port check

* p2p: add comment

* p2p/simulations/adapters: ensure assigned port is in all node records

p2p/discover/v4_udp.go

@@ -169,7 +169,7 @@ func makeEndpoint(addr *net.UDPAddr, tcpPort uint16) rpcEndpoint {
 
 func (t *UDPv4) nodeFromRPC(sender *net.UDPAddr, rn rpcNode) (*node, error) {
 	if rn.UDP <= 1024 {
-		return nil, errors.New("low port")
+		return nil, errLowPort
 	}
 	if err := netutil.CheckRelayIP(sender.IP, rn.IP); err != nil {
 		return nil, err