Overrated if_obytes accounting in 8.4-STABLE

[Eugene Grosbein]

Hi!

Right now outgoint network interface accounting is broken in stable/8
due to incomplete MFC (r247430) of r241037. That MFC was meant to
move if_obytes computation from drbr to distinct drivers.
In fact, it did not remove if_obytes computation drom drbr so it is overrated.

The patch for stable/8 is presented here:
http://www.freebsd.org/cgi/query-pr.cgi?pr=182828

Please fix.

Eugene Grosbein