Add basic IPv4/IPv6 forwarding tests.

[melifaro]

Summary

Add basic tests checking working IPv46 forwarding.

All tests are executed in a per-test VNET jail, with routing-on-a-stick setup.

Tests

IPv4

"Slow" path is enforced by using Stream ID ip option.

• fwd_ip_icmp_iface_fast_success - fastforwarding, routing to the interface, redirects disabled
• fwd_ip_icmp_gw_fast_success - fastforwarding, routing to the gateway, redirects disabled
• fwd_ip_icmp_iface_slow_success - slow forwarding, routing to the interface, redirects disabled
• fwd_ip_icmp_gw_slow_success - slow forwarding, routing to the gateway, redirects disabled

IPv6

"Slow" path is enforced by not disabling redirects.

• fwd_ip6_gu_icmp_iface_fast_success - fastforwarding, routing to interface, redirects disabled
• fwd_ip6_gu_icmp_gw_gu_fast_success - fastforwarding, routing to global unicast gateway, redirects disabled
• fwd_ip6_gu_icmp_gw_ll_fast_success - fastforwarding, routing to link-local gateway, redirects disabled
• fwd_ip6_gu_icmp_iface_slow_success - forwarding, routing to interface, redirects enabled
• fwd_ip6_gu_icmp_gw_gu_slow_success - forwarding, routing to global unicast gateway, redirects enabled
• fwd_ip6_gu_icmp_gw_ll_slow_success - forwarding, routing to global unicast gateway, redirects enabled

Test Plan

kyua test -k /usr/tests/sys/netinet6/Kyuafile forward6
forward6:fwd_ip6_gu_icmp_gw_gu_fast_success  ->  passed  [2.359s]
forward6:fwd_ip6_gu_icmp_gw_gu_slow_success  ->  passed  [2.055s]
forward6:fwd_ip6_gu_icmp_gw_ll_fast_success  ->  passed  [1.625s]
forward6:fwd_ip6_gu_icmp_gw_ll_slow_success  ->  passed  [2.173s]
forward6:fwd_ip6_gu_icmp_iface_fast_success  ->  passed  [1.995s]
forward6:fwd_ip6_gu_icmp_iface_slow_success  ->  passed  [2.230s]

forward:fwd_ip_icmp_gw_fast_success  ->  passed  [0.344s]
forward:fwd_ip_icmp_gw_slow_success  ->  passed  [0.366s]
forward:fwd_ip_icmp_iface_fast_success  ->  passed  [0.361s]
forward:fwd_ip_icmp_iface_slow_success  ->  passed  [0.405s]