ss: prepare rth when killing inet sock

ss: prepare rth when killing inet sock

kill_inet_sock() expects rhn_handle instance is passed
via inet_diag_arg argument. However on the following calling path:

    generic_show_sock
    => show_one_inet_sock
       => kill_inet_sock

rth field of inet_diag_arg is not filled with the address of
rhn_handle instance. As the result ss crashes.

This commit fills the field with newly created rhn_handle
instance.

Changes in v2:
Instead of creating rtn_handle instances for each socket, create
one in upper layer and reuse it.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>