The help information was not added at the time when the function got added.
Fix this and add the missing information to its cli, documentation and bash
completion.

Fixes: db94cc0b ("bpftool: Add support for BPF_CGROUP_INET_SOCK_RELEASE")
Signed-off-by: NLiu Jian <liujian56@huawei.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: NQuentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20210525014139.323859-1-liujian56@huawei.com