net/mlx5: DR, Ignore modify TTL on RX if device doesn't support it

When modifying TTL, packet's csum has to be recalculated.
Due to HW issue in ConnectX-5, csum recalculation for modify
TTL on RX is supported through a work-around that is specifically
enabled by configuration.
If the work-around isn't enabled, rather than adding an unsupported
action the modify TTL action on RX should be ignored.
Ignoring modify TTL action might result in zero actions, so in such
cases we will not convert the match STE to modify STE, as it is done
by FW in DMFS.

This patch fixes an issue where modify TTL action was ignored both
on RX and TX instead of only on RX.

Fixes: 4ff725e1 ("net/mlx5: DR, Ignore modify TTL if device doesn't support it")
Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>