drivers: net: use flow block API

This patch updates flow_block_cb_setup_simple() to use the flow block API.
Several drivers are also adjusted to use it.

This patch introduces the per-driver list of flow blocks to account for
blocks that are already in use.

Remove tc_block_offload alias.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>