Add zfs_refcount_transfer_ownership_many()

When debugging is enabled and a zfs_refcount_t contains multiple holders
using the same key, but different ref_counts, the wrong reference_t may
be transferred.  Add a zfs_refcount_transfer_ownership_many() function,
like the existing zfs_refcount_*_many() functions, to match and transfer
the correct refcount_t;

This issue may occur when using encryption with refcount debugging
enabled.  An arc_buf_hdr_t can have references for both the
hdr->b_l1hdr.b_pabd and hdr->b_crypt_hdr.b_rabd both of which use
the hdr as the reference holder.  When unsharing the buffer the
p_abd should be transferred.

This issue does not impact production builds because refcount holders
are not tracked.

Reviewed-by: Matthew Ahrens <[email protected]>
Signed-off-by: Tom Caputi <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #7219
Closes #8000

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