net/mlx5e: Un-expose functions in en.h

Un-expose functions that are not used outside of their c file.
Make them static.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Link: https://lore.kernel.org/r/20240404173357.123307-6-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>