MFC 1.64: Restore a historical ufs_inactive behavior that respect the RDONLY option, so subsequent call of UFS_TRUNCATE (ffs_truncate) would not panic the system.  This fixes a panic that can happen when mounting a corrputed filesystem read-only, and reading data from it.
MFC 1.64: Restore a historical ufs_inactive behavior that respect
the RDONLY option, so subsequent call of UFS_TRUNCATE (ffs_truncate)
would not panic the system.  This fixes a panic that can happen
when mounting a corrputed filesystem read-only, and reading data
from it.

Reviewed by:	mckusick
Approved by:	re (scottl)

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