datapath: Fix circular dependency between bug.h and kernel.h.

datapath: Fix circular dependency between bug.h and kernel.h.

In Linux 3.4 the definition for BUILD_BUG_ON_NOT_POWER_OF_2 was
moved from kernel.h to bug.h.  On various kernels these header
files include each other in various orders (often through a
long chain of other header files), which can create circular
dependency issues.  Since we not longer need this definition,
this simply removes the backport.

Reported-by: Palo Andi <andi@dis.uniroma1.it>
Signed-off-by: Jesse Gross <jesse@nicira.com>
Conflicts:
	datapath/linux/Modules.mk