Change unix_diag requests to use exact match instead of full dump

Change unix_diag requests to use exact match instead of full dump

* socketutils.c (unix_send_query): Remove NLM_F_DUMP from nlmsg_flags,
initialize udiag_cookie.
* tests/netlink_unix_diag.c (send_query): Remove "family" and "proto"
arguments, add "inode" argument, remove NLM_F_DUMP from nlmsg_flags,
initialize udiag_ino and udiag_cookie.
(check_responses): Add "inode" argument, check inode match.
(main): Pass listening socket inode to send_query and check_responses.