Allow zvol_geom_worker to process BIO_DELETE's

If zvol_geom_start is called with a BIO_DELETE from a thread which can
sleep it queues it for later processing by the zvol_geom_worker. The
zvol_geom_worker didn't have a delete case so would simply loose the bio
hence preventing the original caller from every completing. In addition
an other unknown types would suffer the same fate.

Allow zvol_geom_worker to process BIO_DELETE's via zvol_strategy and
return unsupported for all unknown bio types.

MFC after:	2 weeks
Sponsored by:	Multiplay

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c

@@ -2775,8 +2775,12 @@ zvol_geom_worker(void *arg)
 			break;
 		case BIO_READ:
 		case BIO_WRITE:
+		case BIO_DELETE:
 			zvol_strategy(bp);
 			break;
+		default:
+			g_io_deliver(bp, EOPNOTSUPP);
+			break;
 		}
 	}
 }