- Use if_get_counter() to fetch ifnet statistics.
- Report IFCOUNTER_OQDROPS to linprocfs. Wasn't there before.

Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
simple_httpd: cosmetic cleanups.

Many tab vs space cleanups.
Use setpgid() instead of setpgrp() which is more portable,

MFC after:	5 weeks
Enable ZFS debug flags to be modified via vfs.zfs.debug_flags.

This is primarily only of interest to ZFS developers, but it makes it
easier to get additional debugging.

Submitted by:	gibbs
MFC after:	1 month
Sponsored by:	Spectra Logic
MFSpectraBSD:	517074 on 2011/12/15 (by will), 662343 on 2013/03/20 (by gibbs)