MFC	r252364:

Bring some updates from ufs/ufs_lookup to ext2fs.

Don't set IN_CHANGE and IN_UPDATE on inodes for potentially suspended
file systems.

Only set i_offset in the parent directory's i-node during a lookup for
non-LOOKUP operations.
Relax a VOP assertion for a DELETE lookup.

Move the code from ufs_lookup.c used to do dotdot lookup, into
the helper function. It is supposed to be useful for any filesystem
that has to unlock dvp to walk to the ".." entry in lookup routine.