Generate temporary DH key for testing. DO NOT USE.
Fix a nasty bug with send().
Temporary fiddling until I figure out how to cast shared_ptrs.

I need to pass shared_ptr<udp_link> for expected shared_ptr<link>
(a shared pointer to the derived class instead of base).
Set magic value for the inserted link_receiver.
Some send() helpers.
Suppress assert for testing. DO NOT USE.

This needs fixing.
Remove comment that could lead to overcomplicated code.
Initialize receiving link properly.