Fix 'zfs receive -o' when used with '-e|-d'

Fix 'zfs receive -o' when used with '-e|-d'

When used in conjunction with one of '-e' or '-d' zfs receive options
none of the properties requested to be set (-o) are actually applied:
this is caused by a wrong assumption made about the toplevel dataset
in zfs_receive_one().

Fix this by correctly detecting the toplevel dataset.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #7088

Requires-spl: refs/pull/679/head