MFC r285190:

Fix if_loop so bpfwrite() can use it regardless of the state of
bd_hdrcmplt. As if_loop does not use link-level headers, its behavior
when used by bpfwrite() should be the same regardless of the state of
bd_hdrcmplt. Without this change, libpcap (and other BPF users that
work like it) fail when writing to loopback interfaces.

Approved by: re

Merge r262763, r262767, r262771, r262806 from head:
- Remove rt_metrics_lite and simply put its members into rtentry.
- Use counter(9) for rt_pksent (former rt_rmx.rmx_pksent). This
removes another cache trashing ++ from packet forwarding path.
- Create zini/fini methods for the rtentry UMA zone. Via initialize
mutex and counter in them.
- Fix reporting of rmx_pksent to routing socket.
- Fix netstat(1) to report "Use" both in kvm(3) and sysctl(3) mode.

MFC r285190:

Fix if_loop so bpfwrite() can use it regardless of the state of
bd_hdrcmplt. As if_loop does not use link-level headers, its behavior
when used by bpfwrite() should be the same regardless of the state of
bd_hdrcmplt. Without this change, libpcap (and other BPF users that
work like it) fail when writing to loopback interfaces.

Approved by: re

Merge r262763, r262767, r262771, r262806 from head:
- Remove rt_metrics_lite and simply put its members into rtentry.
- Use counter(9) for rt_pksent (former rt_rmx.rmx_pksent). This
removes another cache trashing ++ from packet forwarding path.
- Create zini/fini methods for the rtentry UMA zone. Via initialize
mutex and counter in them.
- Fix reporting of rmx_pksent to routing socket.
- Fix netstat(1) to report "Use" both in kvm(3) and sysctl(3) mode.