ring: prepare setup_rx_ring_layout for support in v2/v3

Prepare setup_rx_ring_layout for both, v2 and v3. Also do some checks
during compile time if offsets stay the same as we operate on different
union mappings.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
ring: setup_{rx,tx}_ring_layout: use bool for jumbo_support

There's no good reason why we currently waste an 'int' for
jumbo_support while this must better be done as 'bool'.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>