obfs4: filter out kcp bridges when transport is obfs4

in case of KCP the transport.Type is still obfs4, but it has
a different port than obfs4, without this commit KCP enabled
bridges were also considered as valid obfs4 bridges

in theory the same bridge can be running in both obfs4 and KCP
mode and listening on different ports, but the eip-service.json
schema separates this into different transport objects

this fixes a bug where after selecting obfs4 transport it was
trying connect to a KCP enabled bridge with plain obfs4 mode

pkg/vpn/bonafide/gateways.go

@@ -66,6 +66,9 @@ func (gw Gateway) isTransport(transport string) bool {
 	if transport == "kcp" {
 		return gw.Transport == "obfs4" && slices.Contains(gw.Protocols, "kcp")
 	}
+	if transport == "obfs4" {
+		return gw.Transport == "obfs4" && !slices.Contains(gw.Protocols, "kcp")
+	}
 	return transport == "any" || gw.Transport == transport
 }