tools: bpftool: add missing --bpffs to completions

--bpffs is not suggested by bash completions.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/bash-completion/bpftool

@@ -182,7 +182,7 @@ _bpftool()
     if [[ -z $object ]]; then
         case $cur in
             -*)
-                local c='--version --json --pretty'
+                local c='--version --json --pretty --bpffs'
                 COMPREPLY=( $( compgen -W "$c" -- "$cur" ) )
                 return 0
                 ;;