Clarify the meaning of "application-limited" to explicitly
mention that this can include slow sender applicaitons
or slow receiver applications.

Matt Olson notes in Issue NTAP#137:

  It seems like usually "app-limited" refers only to the local app, 
  but if the peer's receive window limits the connection's send 
  rate then we have the same problem where CWnd can grow
 arbitrarily. So, is "app-limited" supposed to also refer to the peer's
 receive window? If so, then this should probably be spelled out.

So we should be explicit that application-limited can refer to sender
or receiver apps that are slower than what cwnd allows.

We should particularly clarify this because the text on this topic
in 7661 is buggy, when it says:

   "application-limited period" for the time when the sender sends less
  than is allowed by the congestion or receiver windows.

This RFC 7661 text is buggy because if the receiver window is
smaller than the congestion window, and the sender sends
an amount equal to the receiver window, then the flow is
application-limited (it is limited by the receiver and receiver
advertised window instead of cwnd).

Co-authored-by: Vidhi Goel <goel.vidhi07@gmail.com>

Co-authored-by: Vidhi Goel <goel.vidhi07@gmail.com>

From @larseggert and @goelvidhi.

Co-authored-by: Lars Eggert <lars@eggert.org>

The latest patch caused a lint error:

draft-ietf-tcpm-rfc8312bis.md:1017:81 MD013/line-length Line length [Expected: 80; Actual: 99]

Fixed by wrapping:

"and thus sends less data than what is allowed by
the sender's congestion window."