btrfs: test send for files with multiple hard links renamed

btrfs: test send for files with multiple hard links renamed

Test that an incremental send operation works if a file that has
multiple hard links has some of its hard links renamed in the send
snapshot, with one of them getting the same path that some other
inode had in the send snapshot.

At the moment this test fails on btrfs and a fix is provived by a
linux kernel patch titled:

  "Btrfs: incremental send, fix wrong unlink path after renaming file"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>