PROCEDURE NetIn(L: Integer);
   EXTERNAL;
{*USER*
 
  This procedure processes inbound messages from a DECNET link other
than the network mailbox. For AMIRTR, this means net messages comming
from other message routers on the net.
  Parameter L is the index into the Link array.
  The design of the message system dictates that messages which cannot
be processed (e.g., unknown addressee) be simply dropped. This makes
error handling easy, at least at this level.
 
    Messages are either:
      1. Sent to destination task (via SMSG), possibly with additional
          action specified in message flags.
      2. Router control messages for this router - passed to DoCtrl for
          processing.
      3. Can't be handled and dropped on the floor.
 
 
  This routine is also involved in link shutdown. Once the program is
notified (via net mailbox) that a link is shutting down, we stop sending
to it. However, pending inbound traffic will complete. Eventually,
we arrive here with an IOSB of NT_ABT or NT_ABO, telling us that
the net data queue has been flushed. At that time, we go ahead and
zap the link structures and declare the link inactive.
 
 }