vm/test: fix action associated to --jit option
vm/test: fix action associated to --jit option

`--jit` long option was resolved as `-m` (such as for `--mem`, but
without even requiring an argument). This commit makes `--jit` point to
`-j` instead, as described in the program help.

iovisor/ubpf,iovisor/ubpf,iovisor/ubpf,iovisor/ubpf,rlane/ubpf,rlane/ubpf