Prevent theoretical double free and leak on get_peer_sock_name.

Variable new_sockname will leak and sockname will be double freed if
both of the cases shown below are true.

1. realloc succeeds and doesn't return the original pointer
2. calling socket_func fails

Signed-off-by: Rami Ylimäki <rami.ylimaki@vincit.fi>
Signed-off-by: Erkki Seppälä <erkki.seppala@vincit.fi>
Reviewed-by: Arnaud Fontaine <arnau@debian.org>
Signed-off-by: Peter Harris <pharris@opentext.com>