Before:
* hand write arg parse
* only accepts one suffix
After:
* use `arg_parse` to parse args
* accepts multi suffixes
Closes#9611.
(cherry picked from commit aa65856ee0)
I'm not sure what was wrong with the old syntax, but I needed to switch
the outer quotes to ' and the inner quotes to " in order for the
completions to work when they weren't explicitly sourced.
Additionally, realized that the overload for __fish_complete_suffix can
be used to get the filtered list of kernel modules from /boot/kernel in
the initial run.
