net/mlx5e: Properly check if hairpin is possible between two functions

The current check relies on function BDF addresses and can get
us wrong e.g when two VFs are assigned into a VM and the PCI
v-address is set by the hypervisor.

Fixes: 5c65c564

 ('net/mlx5e: Support offloading TC NIC hairpin flows')
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reported-by: Alaa Hleihel <alaa@mellanox.com>
Tested-by: Alaa Hleihel <alaa@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>