sock_diag: define destruction multicast groups

These groups will contain socket-destruction events for
AF_INET/AF_INET6, IPPROTO_TCP/IPPROTO_UDP.

Near the end of socket destruction, a check for listeners is
performed.  In the presence of a listener, rather than completely
cleanup the socket, a unit of work will be added to a private
work queue which will first broadcast information about the socket
and then finish the cleanup operation.

Signed-off-by: Craig Gallek <kraig@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/sock_diag.h

@@ -23,4 +23,14 @@ enum {
 	SK_MEMINFO_VARS,
 };
 
+enum sknetlink_groups {
+	SKNLGRP_NONE,
+	SKNLGRP_INET_TCP_DESTROY,
+	SKNLGRP_INET_UDP_DESTROY,
+	SKNLGRP_INET6_TCP_DESTROY,
+	SKNLGRP_INET6_UDP_DESTROY,
+	__SKNLGRP_MAX,
+};
+#define SKNLGRP_MAX	(__SKNLGRP_MAX - 1)
+
 #endif /* _UAPI__SOCK_DIAG_H__ */