cryptodev: fix ABI breakage

cryptodev: fix ABI breakage

In 17.08, the crypto operation was restructured,
and some reserved bytes (5) were added  to have the mempool
pointer aligned to 64 bits, since the structure is expected
to be aligned to 64 bits, allowing future additions with no
ABI breakage needed.

In 18.05, a new 2-byte field was added, so the reserved bytes
were reduced to 3. However, this field was added after the first 3 bytes
of the structure, causing it to be placed in an offset of 4 bytes,
and therefore, forcing the mempool pointer to be placed after 16 bytes,
instead of a 8 bytes, causing unintentionally the ABI breakage.

This commit fixes the breakage, by swapping the reserved bytes
and the private_data_offset field, so the latter is aligned to 2 bytes
and the offset of the mempool pointer returns to its original offset,
8 bytes.

Fixes: 54c836846603 ("cryptodev: set private data for session-less mode")
Cc: stable@dpdk.org
Reported-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Abhinandan Gujjar <abhinandan.gujjar@intel.com>