PROCEDURE MsgIn(VAR Msg: Message_rec);
   EXTERNAL;
{*USER*
 
 This procedure handles messages received from the local node (via VRCD), or
from a remote link (via NtRCV). Routing is the same in either case.
Possibilities are:
 
    1. Message destination is same node (usually testing only):
        If message is a router-control message, give it to RTRCTL.
        Else message is routed directly from here to SMSG. Done.
    2. Message destination is different node:
        Check that we have a link to that node. If not, attempt to
        establish one. Once link is found, send message via NtSND.
 }