bpftool: Clean up _bpftool_once_attr() calls in bash completion

In bpftool's bash completion file, function _bpftool_once_attr() is able
to process multiple arguments. There are a few locations where this
function is called multiple times in a row, each time for a single
argument; let's pass all arguments instead to minimize the number of
function calls required for the completion.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/r/20230405132120.59886-8-quentin@isovalent.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>