http: attach reused parser to correct domain

Reused parsers can be attached to the domain that corresponds to the
active domain when the underlying socket was created, which is not
necessarily correct.

Instead, we attach parsers to the active domain if there is one when
they're reused from the pool.

Refs: https://github.com/nodejs/node/issues/25456

PR-URL: https://github.com/nodejs/node/pull/25459


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>