unix_parse_response: add a safety check
unix_parse_response: add a safety check

* socketutils.c (unix_parse_response): Check that netlink message
is large enough to contain a unix_diag_msg structure.

Saruta/strace,cuviper/strace,Saruta/strace,Saruta/strace,cuviper/strace,Saruta/strace,Saruta/strace,cuviper/strace,cuviper/strace,cuviper/strace