net/mlx5e: Adjustments in the TC offload code towards reuse for SRIOV

Towards reusing the TC offloads code for an SRIOV use-case, change some of the
helper functions to have _nic in their names so it's clear what's NIC unique
and what's general. Also group together the NIC related helpers so we can easily
branch per the use-case in downstream patch.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>