zfs send -p send properties only for snapshots that are actually sent

... as opposed to sending properties of all snapshots of the relevant
filesystem.  The previous behavior results in properties being set on
all snapshots on the receiving side, which is quite slow.
More details are here:
  http://thread.gmane.org/gmane.comp.file-systems.openzfs.devel/346

Behavior of zfs send -R is not changed.

lib/libzfs/libzfs_sendrecv.c

@@ -561,6 +561,8 @@ typedef struct send_data {
 	const char *fromsnap;
 	const char *tosnap;
 	boolean_t recursive;
+	boolean_t seenfrom;
+	boolean_t seento;
 
 	/*
 	 * The header nvlist is of the following format:
@@ -595,20 +597,39 @@ send_iterate_snap(zfs_handle_t *zhp, void *arg)
 	uint64_t guid = zhp->zfs_dmustats.dds_guid;
 	char *snapname;
 	nvlist_t *nv;
+	boolean_t isfromsnap, istosnap;
 
 	snapname = strrchr(zhp->zfs_name, '@')+1;
+	isfromsnap = (sd->fromsnap != NULL &&
+	    strcmp(sd->fromsnap, snapname) == 0);
+	istosnap = (sd->tosnap != NULL && (strcmp(sd->tosnap, snapname) == 0));
 
-	VERIFY(0 == nvlist_add_uint64(sd->parent_snaps, snapname, guid));
 	/*
 	 * NB: if there is no fromsnap here (it's a newly created fs in
 	 * an incremental replication), we will substitute the tosnap.
 	 */
-	if ((sd->fromsnap && strcmp(snapname, sd->fromsnap) == 0) ||
-	    (sd->parent_fromsnap_guid == 0 && sd->tosnap &&
-	    strcmp(snapname, sd->tosnap) == 0)) {
+	if (isfromsnap || (sd->parent_fromsnap_guid == 0 && istosnap)) {
 		sd->parent_fromsnap_guid = guid;
 	}
 
+	if (!sd->recursive) {
+		if (!sd->seenfrom && isfromsnap) {
+			sd->seenfrom = B_TRUE;
+			zfs_close(zhp);
+			return (0);
+		}
+
+		if (sd->seento || !sd->seenfrom) {
+			zfs_close(zhp);
+			return (0);
+		}
+
+		if (istosnap)
+			sd->seento = B_TRUE;
+	}
+
+	VERIFY(0 == nvlist_add_uint64(sd->parent_snaps, snapname, guid));
+
 	VERIFY(0 == nvlist_alloc(&nv, NV_UNIQUE_NAME, 0));
 	send_iterate_prop(zhp, nv);
 	VERIFY(0 == nvlist_add_nvlist(sd->snapprops, snapname, nv));