Proper check if divert(4) module is present by the relevant tests

[syrinx]

Summary

Fix the netinet/netinet6 divert tests falsely reporting
'ipdivert module is not loaded' when the divert module is built
in the kernel

Sponsored by: Axiado

Test Plan

On a FreeBSD system with

options IPFIREWALL
options IPDIVERT

enabled in the kernel config file, run

kyua test -k /usr/tests/sys/netinet/Kyuafile divert:ipdivert_ip_output_remote_success
kyua test -k /usr/tests/sys/netinet6/Kyuafile divert:ipdivert_ip6_output_remote_success

and verify the tests are passing.