Documentation: replace __sk_run_filter with __bpf_prog_run

__sk_run_filter has been renamed as __bpf_prog_run, so replace them in comments

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>