Fix: Correctly flag UDP streams in net/connect #1620

[tttuuu888]

This change adds the JANET_STREAM_UDPSERVER flag to :datagram streams created by net/connect.
Previously, these streams were missing the flag, causing functions like net/send-to to fail with a "bad stream" error.

Thank you.

[bakpakin]

Thanks @tttuuu888 , this looks like a good improvement. I suppose although a UDP connection isn't really a "server", the net/send-to and net/recv-from would work fine in this case.