Prevent tincd from sending packets to unexpecting nodes

Make tincd recognize when it was asleep and close connections to it's
peers. This happens when e.g. RoadWarrior has been suspended for
"longer" time period. After resume, it will start to communicate
with it's peers using the contextes it had before suspend.

On the other side, the nodes closed the connections since PingTimeout
and/or TCP connection went down.

Sending data to such unaware (sptps mostly) nodes will cause
havoc in the logs. Misleading the developers to wrong assumptions
that something is wrong with sptps.

# Conflicts:
#	src/net.c