samples/bpf: Update bpf loader for cgroup section names

Add support for section names starting with cgroup/skb and cgroup/sock.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>