Merge r259528, r259528, r260295.

r259528:
  Simplify contiguous mask checking.

  Suggested by: glebius

r260228:
  Remove useless register variable modifiers.
  Do some more style(9).

r260295:
  Change semantics for rnh_lookup() function: now
  it performs exact match search, regardless of netmask existance.
  This simplifies most of rnh_lookup() consumers.

  Fix panic triggered by deleting non-existent host route.

  PR:           kern/185092
  Submitted by: Nikolay Denev <ndenev at gmail.com>