rtsock functionality tests: [[ https://reviews.freebsd.org/D22860 | D22860 ]].
Before:
```
10:02 [2] m@devel2 s kyua test -k /usr/obj/usr/home/melifaro/free/head/amd64.amd64/tests/sys/net/routing/Kyuafile
test_rtsock_l3:rtm_add_v4_gw_direct_success -> passed [0.011s]
test_rtsock_l3:rtm_add_v6_gu_gw_gu_direct_success -> passed [0.005s]
test_rtsock_l3:rtm_del_v4_prefix_nogw_success -> passed [0.005s]
test_rtsock_l3:rtm_del_v6_gu_prefix_nogw_success -> failed: /usr/home/melifaro/free/head/tests/sys/net/routing/test_rtsock_l3.c:123: NETMASK sa diff: overall memcmp() reports diff for af 28 offset 2 [0.005s]
test_rtsock_l3:rtm_get_v4_empty_dst_failure -> passed [0.002s]
test_rtsock_l3:rtm_get_v4_exact_success -> passed [0.004s]
test_rtsock_l3:rtm_get_v4_hostbits_failure -> passed [0.005s]
test_rtsock_l3:rtm_get_v4_lpm_success -> passed [0.005s]
test_rtsock_lladdr:rtm_add_v4_gu_lle_success -> passed [0.005s]
test_rtsock_lladdr:rtm_add_v6_gu_lle_success -> passed [0.003s]
test_rtsock_lladdr:rtm_add_v6_ll_lle_success -> passed [0.003s]
test_rtsock_lladdr:rtm_del_v4_gu_lle_success -> passed [0.005s]
test_rtsock_lladdr:rtm_del_v6_gu_lle_success -> passed [0.003s]
test_rtsock_lladdr:rtm_del_v6_ll_lle_success -> passed [0.003s]
```
After:
```
9:59 [0] m@devel0 s kyua test -k /usr/obj/usr/home/melifaro/free/head/amd64.amd64/tests/sys/net/routing/Kyuafile
test_rtsock_l3:rtm_add_v4_gw_direct_success -> passed [0.013s]
test_rtsock_l3:rtm_add_v6_gu_gw_gu_direct_success -> passed [0.007s]
test_rtsock_l3:rtm_del_v4_prefix_nogw_success -> passed [0.005s]
test_rtsock_l3:rtm_del_v6_gu_prefix_nogw_success -> failed: /usr/home/melifaro/free/head/tests/sys/net/routing/test_rtsock_l3.c:123: NETMASK sa diff: overall memcmp() reports diff for af 28 offset 2 [0.005s]
test_rtsock_l3:rtm_get_v4_empty_dst_failure -> passed [0.002s]
test_rtsock_l3:rtm_get_v4_exact_success -> passed [0.005s]
test_rtsock_l3:rtm_get_v4_hostbits_failure -> passed [0.005s]
test_rtsock_l3:rtm_get_v4_lpm_success -> passed [0.005s]
test_rtsock_lladdr:rtm_add_v4_gu_lle_success -> passed [0.005s]
test_rtsock_lladdr:rtm_add_v6_gu_lle_success -> passed [0.003s]
test_rtsock_lladdr:rtm_add_v6_ll_lle_success -> passed [0.003s]
test_rtsock_lladdr:rtm_del_v4_gu_lle_success -> passed [0.005s]
test_rtsock_lladdr:rtm_del_v6_gu_lle_success -> passed [0.003s]
test_rtsock_lladdr:rtm_del_v6_ll_lle_success -> passed [0.003s]
```
(rtm_del_v6_gu_prefix_nogw_success is working, but complaining about not fully zeroing IPv6 netmask SA in the output, which needs to be fixed as a separate issue).