net/mlx5e: Move mlx5e_init_l2_addr to en_main

Move the function declaration of mlx5e_init_l2_addr to en/fs.h, rename
to mlx5e_fs_init_l2_addr to align with the fs API functions naming
convention and let it take mlx5e_flow_steering as arguments while keeping
implementation at en_fs.c file. This helps maintain a clean driver code
and avoids unnecessary dependencies.

Signed-off-by: Lama Kayal <lkayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>