doc: add fields enum for modify action in flow guide
doc: add fields enum for modify action in flow guide

Fix the documentation about the MODIFY_FIELD flow action.
1. Include the rte_flow_field_id enumeration reference to point
to the full list of all supported Field IDs available.
2. Correct the formatting of the MODIFY_FIELD action and the
destination/source field definition tables.

Fixes: 73b68f4c54a0 ("ethdev: introduce generic modify flow action")
Cc: stable@dpdk.org

Signed-off-by: Alexander Kozyrev <a103889f73a7af0066377584f3d0eb32f9983c2e@nvidia.com>
Acked-by: Viacheslav Ovsiienko <5b8db9bb93a9a9aefc8828f79604d1fe963a53dd@nvidia.com>
Reviewed-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk