3744 zfs shouldn't ignore errors unmounting snapshots
Submitted by:   Will Andrews <willa@spectralogic.com>
Reviewed by:    Matthew Ahrens <mahrens@delphix.com>

@@ -342,11 +342,11 @@
 extern int zfs_secpolicy_snapshot_perms(const char *name, cred_t *cr);
 extern int zfs_secpolicy_rename_perms(const char *from,
     const char *to, cred_t *cr);
 extern int zfs_secpolicy_destroy_perms(const char *name, cred_t *cr);
 extern int zfs_busy(void);
-extern void zfs_unmount_snap(const char *);
+extern int zfs_unmount_snap(const char *);
 extern void zfs_destroy_unmount_origin(const char *);
 
 /*
  * ZFS minor numbers can refer to either a control device instance or
  * a zvol. Depending on the value of zss_type, zss_data points to either