daemon: free listen_addr before returning

daemon: free listen_addr before returning

We build up a string list of listen addresses from the command-line
arguments, but never free it. This causes t5811 to complain of a leak
(though curiously it seems to do so only when compiled with gcc, not
with clang).

To handle this correctly, we have to do a little refactoring:

  - there are two exit points from the main function, depending on
    whether we are entering the main loop or serving a single client
    (since rather than a traditional fork model, we re-exec ourselves
    with the extra "--serve" argument to accommodate Windows).

    We don't need --listen at all in the --serve case, of course, but it
    is passed along by the parent daemon, which simply copies all of the
    command-line options it got.

  - we just "return serve()" to run the main loop, giving us no chance
    to do any cleanup

So let's use a "ret" variable to store the return code, and give
ourselves a single exit point at the end. That gives us one place to do
cleanup.

Note that this code also uses the "use a no-dup string-list, but
allocate strings we add to it" trick, meaning string_list_clear() will
not realize it should free them. We can fix this by switching to a "dup"
string-list, but using the "append_nodup" function to add to it (this is
preferable to tweaking the strdup_strings flag before clearing, as it
puts all the subtle memory-ownership code together).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>