MFC r317702, r317847, r318307

MFC r317702, r317847, r318307

r317702:
cxgbe(4): Support routines for Tx traffic scheduling.

- Create a new file, t4_sched.c, and move all of the code related to
  traffic management from t4_main.c and t4_sge.c to this file.
- Track both Channel Rate Limiter (ch_rl) and Class Rate Limiter (cl_rl)
  parameters in the PF driver.
- Initialize all the cl_rl limiters with somewhat arbitrary default
  rates and provide routines to update them on the fly.
- Provide routines to reserve and release traffic classes.

r317847:
cxgbe(4): The Tx scheduler initialization either works or doesn't.  It
doesn't need a refresh in either case.

r318307:
cxgbe(4): Avoid an out of bounds access when an attempt to unbind a tx
queue from a traffic class fails.

Sponsored by:	Chelsio Communications

git-svn-id: svn://svn.freebsd.org/base/stable/10@318851 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f