examples/l2fwd-crypto: fix padding calculation

For padding calculation, it is necessary to know if algorithm
is a block cipher or stream cipher algorithm, and know the
block size for the algorithm.

In the application, this block size should be only the
cipher block size, but if authentication was used too,
it was being overwritten by the authentication block size,
which is not needed.

Fixes: 27cf2d1b18e1 ("examples/l2fwd-crypto: discover capabilities")
Cc: stable@dpdk.org
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Fan Zhang <roy.fan.zhang@intel.com>