Improve postmaster's logging of listen socket creation.

Improve postmaster's logging of listen socket creation.

When one of the kernel calls in the socket()/bind()/listen() sequence
fails, include the specific address we're trying to bind to in the log
message.  This greatly eases debugging of network misconfigurations.

Also, after successfully setting up a listen socket, report its address
in the log, to ease verification that the expected addresses were bound.
There was some debate about whether to print this message at LOG level or
only DEBUG1, but the majority of votes were for the former.

Discussion: https://postgr.es/m/9564.1489091245@sss.pgh.pa.us