examples/ipsec-secgw: fix anonymous union initialization

examples/ipsec-secgw: fix anonymous union initialization

In icc 14.0, compilation was broken:

examples/ipsec-secgw/sa.c(212): error: a designator for an anonymous
union member can only appear within braces corresponding to that anonymous union
        .cipher = { RTE_CRYPTO_CIPHER_OP_ENCRYPT, RTE_CRYPTO_CIPHER_AES_CBC,
         ^

The member in anonymous union initialization should be inside '{}',
otherwise it will report an error.

Fixes: d299106e8e31 ("examples/ipsec-secgw: add IPsec sample application")

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>