Merge r267361:

Merge r267361:
  Improve logic besides net.bpf.optimize_writers.
  Direct bpf(4) consumers should now work fine with this tunable turned on.
  In fact, the only case when optimized_writers can change program
  behavior is direct bpf(4) consumer setting its read filter to
  catch-all one.

Sponsored by:	Yandex LLC

git-svn-id: svn://svn.freebsd.org/base/stable/9@275608 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f