refactoring ip_output() and the L2 _output()

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

Hi,

The mail subject may recall someone an old thread:
https://mail-index.netbsd.org/tech-net/2013/02/01/msg003847.html

Yes, I'm taking over the task :)


http://www.netbsd.org/~ozaki-r/refactor_l2_output.diff

The patch is basically the same as dyoung's patch with some
tweaks to make it work on -current; it gets rid of route
lookups from L2 output routines such as ether_output
and puts them between ip_output and L2 output routines.

One known issue of the change is that it adds an mbuf flag
to tell ether_output that mbuf is to be set MPLS ether
type. I don't think it's the best way but I don't have
another better approach for now.

Any comments or suggestions are welcome.

Thanks,
  ozaki-r