fixing TestServerSetupConn

We can't pass errProtoHandshakeError here, because the framework uses
`Is` for testing, and that would need `As`. We can however test how
it works for internal errors, which is the most typical case.

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

p2p/server_test.go

@@ -410,11 +410,11 @@ func TestServerSetupConn(t *testing.T) {
 			wantCloseErr: DiscUnexpectedIdentity,
 		},
 		{
-			tt:           &setupTransport{pubkey: clientpub, protoHandshakeErr: errProtoHandshakeError},
+			tt:           &setupTransport{pubkey: clientpub, protoHandshakeErr: DiscTooManyPeers},
 			dialDest:     enode.NewV4(clientpub, nil, 0, 0),
 			flags:        dynDialedConn,
 			wantCalls:    "doEncHandshake,doProtoHandshake,close,",
-			wantCloseErr: errProtoHandshakeError,
+			wantCloseErr: DiscTooManyPeers,
 		},
 		{
 			tt:           &setupTransport{pubkey: srvpub, phs: protoHandshake{ID: crypto.FromECDSAPub(srvpub)[1:]}},