unetd: fix command injection vulnerability

Properly escape shell variables `out_file` and `bin_path` within
`package/network/services/unetd/files/unet.uc` by replacing any internal single
quotes and wrapping them in single quotes to prevent potential command
injection when passing arguments to `sh -c`.

Signed-off-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Co-authored-by: manupawickramasinghe <73810867+manupawickramasinghe@users.noreply.github.com>

Author: google-labs-jules[bot]