kernel -- ccd: Concatenated disk MPLOCK rework.

* Remove freelist of ccdbuf structures; kmalloc is good enough for them,
  removes a global list.

* Rework ccdlock/ccdunlock to use a real lockmgr lock rather than a
  hand-rolled "lock" in the flags field.

* Mark ccd disk D_MPSAFE; calls disk strategy routines without the MPLOCK.

* Remove mplock from ccdiodone biodone callback; use ccdlock() on the
  softcontroller instead.

* Remove unneeded critical section around ccdstart and in ccdioctl.

* Remove mplock2.h.

* Remove cb_freenext linkage from ccd buffers.
Remove some emacs variable settings.
if: Move IFF_OACTIVE bit into ifaltq; prepare multiple TX queues support

ifaltq.altq_hw_oactive is now used to record that NIC's TX queue is full.
IFF_OACTIVE is removed from kernel.  User space IFF_OACTIVE is kept for
compability.

ifaltq.altq_hw_oactive should not be accessed directly.  Following set of
functions are provided and should be used:
ifq_is_oactive(ifnet.if_snd)  - Whether NIC's TX queue is full or not
ifq_set_oactive(ifnet.if_snd) - NIC's TX queue is full
ifq_clr_oactive(ifnet.if_snd) - NIC's TX queue is no longer full