bpftool: Update bash completion for "bpftool feature" command

Update bash completion for "bpftool feature" command with the new
argument: "full".

Signed-off-by: Michal Rostecki <mrostecki@opensuse.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20200226165941.6379-5-mrostecki@opensuse.org