Add basic psock hooks for UDP sockets. This allows adding and removing sockets, as well as automatic removal on unhash and close. Change-Id: Id0e35e63672540015a1789d7b0cee7cc24c597ab Signed-off-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200309111243.6982-8-lmb@cloudflare.com