tests/mac_ipacl: restore sysctls after modification

While here, use 'required_kmods' instead of ad-hoc
checks.

Signed-off-by: Siva Mahadevan <me@svmhdvn.name>

Reviewed by: markj
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Pull request: https://github.com/freebsd/freebsd-src/pull/1856

(cherry picked from commit 79042fd7ed4187d2a74e37618f6fd77f448ca353)