MINOR: stream-int: replace si_cant_put() with si_rx_room_{blk,rdy}()

Remaining calls to si_cant_put() were all for lack of room and were
turned to si_rx_room_blk(). A few places where SI_FL_RXBLK_ROOM was
cleared by hand were converted to si_rx_room_rdy().

The now unused si_cant_put() function was removed.
diff --git a/src/dns.c b/src/dns.c
index 4ceda4d..57bec21 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -2030,7 +2030,7 @@
 			/* let's try again later from this session. We add ourselves into
 			 * this session's users so that it can remove us upon termination.
 			 */
-			si->flags |= SI_FL_RXBLK_ROOM;
+			si_rx_room_blk(si);
 			return 0;
 		}
 		/* fall through */