bpf: fix comment typo

o s/bpf_bpf_get_socket_cookie/bpf_get_socket_cookie

Signed-off-by: Alexander Alemayhu <alexander@alemayhu.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>