net: diag: Add the ability to destroy a socket.

This patch adds a SOCK_DESTROY operation, a destroy function
pointer to sock_diag_handler, and a diag_destroy function
pointer.  It does not include any implementation code.

[Backport of net-next 64be0aed59ad519d6f2160868734f7e278290ac1]

Change-Id: Ia459d14b7368624adda225c4ebd55f4fc40fc02e
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Git-commit: d60326cb49d76f60ef8c742944a58136ddfd0f63
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Ashwanth Goli <ashwanth@codeaurora.org>