bpf: program to load and attach sock_ops BPF progs

The program load_sock_ops can be used to load sock_ops bpf programs and
to attach it to an existing (v2) cgroup. It can also be used to detach
sock_ops programs.

Examples:
    load_sock_ops [-l] <cg-path> <prog filename>
	Load and attaches a sock_ops program at the specified cgroup.
	If "-l" is used, the program will continue to run to output the
	BPF log buffer.
	If the specified filename does not end in ".o", it appends
	"_kern.o" to the name.

    load_sock_ops -r <cg-path>
	Detaches the currently attached sock_ops program from the
	specified cgroup.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>