[balance] Make balance service bit more aggressive
[balance] Make balance service bit more aggressive

To make it bit less likely that user runs out of
allocatable space, let's start the balance already if
there is at least 75% of the total space allocated.

Signed-off-by: Kalle Jokiniemi <00a0ccb0d5d1dac2286489d88c3bc125957675d2@jolla.com>

sailfishos/btrfs-balancer,izh1979/btrfs-balancer,sailfishos/btrfs-balancer,izh1979/btrfs-balancer