MINOR: tcp: When binding socket, attempt to reuse one from the old proc.

MINOR: tcp: When binding socket, attempt to reuse one from the old proc.

Try to reuse any socket from the old process, provided by the "-x" flag,
before binding a new one, assuming it is compatible.
"Compatible" here means same address and port, same namspace if any,
same interface if any, and that the following flags are the same :
LI_O_FOREIGN, LI_O_V6ONLY and LI_O_V4V6.
Also change tcp_bind_listener() to always enable/disable socket options,
instead of just doing so if it is in the configuration file, as the option
may have been removed, ie TCP_FASTOPEN may have been set in the old process,
and removed from the new configuration, so we have to disable it.