Changes the IP address to bind to for dtls_server.c to be "::" or optionally
"0.0.0.0" if the preprocessor symbol FORCE_IPV4 is defined.
Also changes the destinaton IP address for dtls_client.c to be "::1" or if
FORCE_IPV4 symbol is defined "127.0.0.1".
This change allows on compilation dtls_server.c and dtls_client.c to both be
compiled to use either IPv4 or IPv6 so out of the box they will work together
without problem, and to avoid dtls_server.c binding to IPv6 and dtls_client.c
binding to IPv4.
5c0204ef62