ethdev: update modify field flow action

ethdev: update modify field flow action

The generic modify field flow action introduced in [1] has
some issues related to the immediate source operand:

  - immediate source can be presented either as an unsigned
    64-bit integer or pointer to data pattern in memory.
    There was no explicit pointer field defined in the union.

  - the byte ordering for 64-bit integer was not specified.
    Many fields have shorter lengths and byte ordering
    is crucial.

  - how the bit offset is applied to the immediate source
    field was not defined and documented.

  - 64-bit integer size is not enough to provide IPv6
    addresses.

In order to cover the issues and exclude any ambiguities
the following is done:

  - introduce the explicit pointer field
    in rte_flow_action_modify_data structure

  - replace the 64-bit unsigned integer with 16-byte array

  - update the modify field flow action documentation

Appropriate deprecation notice has been removed.

[1] commit 73b68f4c54a0 ("ethdev: introduce generic modify flow action")

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>