gve: rename gve_xdp_xmit to gve_xdp_xmit_gqi

In preparation for XDP DQ support, the gve_xdp_xmit callback needs to
be generalized for all queue formats. This patch renames the GQ-specific
function to gve_xdp_xmit_gqi, and introduces a new gve_xdp_xmit callback
which branches on queue format.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>