The existing function inet_show_netlink sends tcp-diag request and
then receives back the response and prints it on the screen.

The sock-diag and legacy tcp-diag have different request types, but
report sockets in the same format. In order to support both it's
convenient to split the code into sending and receiving parts.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>