virtual_oss: Clean up rcorder

sndiod is part of audio/sndio, so we should avoid referencing a port
utility from base.

We should also require NETWORKING for the service to start, since
virtual_oss can be configured to send audio through the network.

Sponsored by: The FreeBSD Foundation
MFC after: 1 day
Reviewed by: des, markj, emaste
Differential Revision: https://reviews.freebsd.org/D53019

(cherry picked from commit 188ddc15e5460b3abfb2ad5492557911465bedc1)