Revert "rtsp-server: Switch around sendonly/recvonly attributes"

Revert "rtsp-server: Switch around sendonly/recvonly attributes"

This reverts commit 3d275b1345b76151418e3f56ed014d9089ac1a57.

While RFC 3264 (SDP) says that sendonly/recvonly are from the point of view of
the requester, the actual RTSP RFCs (RFC 2326 / 7826) disagree and say
the opposite, just like the ONVIF standard.

Let's follow those RFCs as we're doing RTSP here, and add a property at
a later time if needed to switch to the SDP RFC behaviour.

https://bugzilla.gnome.org/show_bug.cgi?id=793964