backups: enforce estimated upper limit on extracted files count
backups: enforce estimated upper limit on extracted files count

Do not allow (compromised) source VM to use all inodes.

woju/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin