LU-1812 fsfilt: ext4_free_blocks() has changed slightly

LU-1812 fsfilt: ext4_free_blocks() has changed slightly

ext4_free_blocks() now takes a buffer_head and explicit flags instead
of just metadata.  Test the presence of the buffer_head argument to
determine which ext4_free_blocks() is available.

see kernel commit e6362609b6c71c5b802026be9cf263bbdd67a50e

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Signed-off-by: chas williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Change-Id: I925df73a054613469866ec025ae412ead0ce9e56
Reviewed-on: http://review.whamcloud.com/4991
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Hudson
Reviewed-by: Christopher J. Morrone <chris.morrone.llnl@gmail.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>