net/mlx5: DR, Refactor ICMP STE builder

Reworked ICMP tag builder to better handle ICMP v4/6 fields and avoid unneeded
code duplication and 'if' statements, removed unused macro, changed bitfield
of len 8 to u8.

Signed-off-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>