netlink: remove netlink_broadcast_filtered

No users in tree since commit a3498436b3a0 ("netns: restrict uevents"),
so remove this functionality.

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
2 files changed