dsched_fq - Refactor fqp allocation/destruction

dsched_fq - Refactor fqp allocation/destruction

* Accept another argument for fqp allocation which is the corresponding
  fqmp. This is internally stored for proper self-removal out of the
  fqmp list on destruction.

* This parameter is also used to link the fqp into the fqmp list
  automatically on creation, avoiding code duplication and deadlocking.

* Changed the destruction refcount to -0x400 instead of -3 to make
  tracking of these cases simpler and not confuse them with bad
  refcounting.

* NOTE: this also fixes the longstanding issue of an eventual panic
  after a number of policy switches to/from fq.

Reported-by: Antonio Huete (tuxillo@)