block: use fallocate(FALLOC_FL_ZERO_RANGE) in handle_aiocb_write_zeroes

block: use fallocate(FALLOC_FL_ZERO_RANGE) in handle_aiocb_write_zeroes

This efficiently writes zeroes on Linux if the kernel is capable enough.
FALLOC_FL_ZERO_RANGE correctly handles all cases, including and not
including file expansion.

CC: Kevin Wolf <[email protected]>
CC: Stefan Hajnoczi <[email protected]>
CC: Peter Lieven <[email protected]>
CC: Fam Zheng <[email protected]>
Signed-off-by: Denis V. Lunev <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>