examples/l2fwd-crypto: fix ambiguous input key size

examples/l2fwd-crypto: fix ambiguous input key size

Some crypto algorithms support more than one key size
(including cipher key, authentication key, IV and AAD),
but the app was using always the minimum size.

These changes allows the user to use an specific size,
either from the string provided with cipher_key, auth_key, iv and ADD
parameters, or from the values provided with cipher_key_random_size,
auth_key_random_size, iv_random_size and aad_random_size.

This also allows the user to specify the digest size.

Fixes: 1df9c0109f4c ("examples/l2fwd-crypto: parse key parameters")

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Tested-by: Min Cao <min.cao@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>