MFC 258178:

MFC 258178:

Improve robustness of the Xen balloon driver.

sys/dev/xen/balloon/balloon.c:
	Remove unused and commented out code.

	Fix deadlock caused by performing a sleepable malloc
	while holding the balloon mutex.

	Perform proper accounting of the memory used by the domain.

Submitted by:	Roger Pau Monné
Sponsored by:	Citrix Systems R&D
Reviewed by:	gibbs
Approved by:	gibbs (mentor)
Approved by:	re (gjb)

git-svn-id: svn://svn.freebsd.org/base/stable/10@258997 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f