HTTPSession options that require special logic should not be set by the StreamlinkOptions class. This PR therefore moves the logic into new HTTPSession class methods where it actually belongs and also fixes two minor things: lost network interface information when disabling DH key exchange (since a new HTTPS adapter will be mounted) and slightly broken unset logic for the ipv4/ipv6 session options (which is irrelevant for the CLI, as it can only set).

This branch is meant as a preparation for #6792, which will be rebased after merging to master, as that work also adds a new class method for loading cookies from a file. These issues here were noticed while working on #6792.