UnetSocket should use `REMOTE` as datagram service provider for UnetStack 5

[mchitre]

In UnetStack 5, agents providing the REMOTE service also provide the DATAGRAM service. So, if a REMOTE service provider also provides DATAGRAM service, it should be preferentially picked as the datagram service provider for UnetSocket. This will ensure compatibility with older versions of UnetStack as well.

Update needed for:

• Python
• C
• Javascript