mobile: UDP connections can wedge on IP address changes

[kegsay]

DTLS connections are preserved for as long as possible. If a connection is made when only local addresses are available (e.g 192.168) and then the IP address changes, the client does not pick up the IP change resulting in errors like:

write udp: invalid argument

This is caused by the UDP header setting a private IP space (192.168.) as the sender, when communicating with a public IP address. The library should pick this up and reset the connection when this happens.