xfs: detect incorrect gaps in rmap btree

Following in the theme of the last two patchsets, this one strengthens
the rmap btree record checking so that scrub can count the number of
space records that map to a given owner and that do not map to a given
owner.  This enables us to determine exclusive ownership of space that
can't be shared.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
-----BEGIN PGP SIGNATURE-----
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=jpXW
-----END PGP SIGNATURE-----