ss: handle socket diag request in a separate function

It will be reused to show netlink sockets

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
ss: create a function to print info about netlink sockets

It will be reused for printing info about netlink sockets, when
socket diag is used for retrieving information.

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
ss: show destination address for netlink sockets

A netlink socket may be connected to a specific group.

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
ss: Get netlink sockets info via sock-diag (v2)

v2: update netlink_diag.h

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>