async_hooks,http: fix socket reuse with Agent

Under very specific circumstances the `http` implementation
could be brought to crash, because the Agent did not re-assign
the async id field properly after setting up a socket for reuse.

Fixes: https://github.com/nodejs/node/issues/13325
PR-URL: https://github.com/nodejs/node/pull/13348


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>