Revert "performance/write-behind: Changed default value of option disable-till to 0"
Revert "performance/write-behind: Changed default value of option disable-till to 0"

This reverts commit e6c35f74ff4a204cf016ebf201a2630b331f9434.

This commit is found to trigger spurious self heal by causing flush and writev to get
reordered. Reverting as a workaround.

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster