net/mlx5e: Use vhca id as the hairpin peer identifier

The peer vhca id spans less bits vs the ifindex and can
well serve for the hairpin hash key, move to use that.

This is a pre-step to put more info into the hairpin hash
key in downstream patch while keeping it at 32 bits.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>