Merge 1.12 of pf_lb.c from OpenBSD, with some changes. Original commit:

  date: 2010/02/04 14:10:12;  author: sthen;  state: Exp;  lines: +24 -19;
  pf_get_sport() picks a random port from the port range specified in a
  nat rule. It should check to see if it's in-use (i.e. matches an existing
  PF state), if it is, it cycles sequentially through other ports until
  it finds a free one. However the check was being done with the state
  keys the wrong way round so it was never actually finding the state
  to be in-use.

  - switch the keys to correct this, avoiding random state collisions
  with nat. Fixes PR 6300 and problems reported by robert@ and viq.

  - check pf_get_sport() return code in pf_test(); if port allocation
  fails the packet should be dropped rather than sent out untranslated.

  Help/ok claudio@.

Some additional changes to 1.12:

- We also need to bzero() the key to zero padding, otherwise key
  won't match.
- Collapse two if blocks into one with ||, since both conditions
  lead to the same processing.
- Only naddr changes in the cycle, so move initialization of other
  fields above the cycle.
- s/u_intXX_t/uintXX_t/g

PR:		kern/181690
Submitted by:	Olivier Cochard-Labbé <olivier cochard.me>
Sponsored by:	Nginx, Inc.