According to
http://pubs.opengroup.org/onlinepubs/009695399/functions/connect.html
for a "socket [that] has not already been bound to a local address,
connect() shall bind it to an address which, unless the socket's address
family is AF_UNIX, is an unused local address."

...and use it in POSIX sendto() function.

A client should not require to explicitly call bind() to receive packets, but is expected to receive replies sent to the ephemeral port that was selected as a source port by the UDP implementation.

in6addr_any and in6addr_loopback are of type in6_addr