net/mlx5e: Move mod hdr allocation to a single place

[ Upstream commit d9581e2f ]

Move mod hdr allocation chunk from parse_tc_fdb_actions() and
parse_tc_nic_actions() to a shared function.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Maor Dickman <maord@nvidia.com>
Reviewed-by: Oz Shlomo <ozsh@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Stable-dep-of: 0c101a23 ("net/mlx5e: Fix pedit endianness")
Signed-off-by: Sasha Levin <sashal@kernel.org>