Stop ignoring ERELOOKUP from VOP_INACTIVE()

When possible, relock the vnode and retry inactivation. Only vunref() is
required not to drop the vnode lock, so handle it specially by not retrying.

This is a part of the efforts to ensure that unlinked not referenced vnode
does not prevent inode from reusing.

Reviewed by: chs, mckusick
Tested by: pho
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation