Update draft-ietf-quic-recovery.md

draft-ietf-quic-recovery.md

@@ -528,7 +528,7 @@ When a PTO timer expires, a sender MUST send at least one ack-eliciting packet
 in the packet number space as a probe, unless there is no data available to
 send.  An endpoint MAY send up to two full-sized datagrams containing
 ack-eliciting packets, to avoid an expensive consecutive PTO expiration due
-to a single lost datagram.
+to a single lost datagram or transmit data from multiple packet number spaces.
 
 In addition to sending data in the packet number space for which the timer
 expired, the sender SHOULD send ack-eliciting packets from other packet