Remove meaningless RTF_UP check

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

Hi,

There is a questionable code in ip_hresolv_output:
  http://nxr.netbsd.org/xref/src/sys/netinet/ip_output.c#230

As the comment says, checking RTF_UP and doing re-rtalloc1
is questionable. IIUC, it's meaningless because:

- An obtained rtentry is ensured that it's always RTF_UP
  by rtcache, rtalloc1 and rtlookup. If the rtentry isn't changed
  (RTF_UP gets dropped) during processing, the check should be
  unnecessary
- Even if not, i.e., an obtained rtentry can be changed during
  processing, checking only at the point doesn't help; the
  rtentry can be changed after the check

So I think we can get rid of it. Of course, in the future
we should ensure that RTF_UP isn't dropped if someone
is using it somehow once we remove the global locks.

Here is a patch:
  http://www.netbsd.org/~ozaki-r/remove-RTF_UP-check.diff

Any comments?

  ozaki-r