examples/l2fwd-crypto: rename period parameter

examples/l2fwd-crypto: rename period parameter

L2fwd-crypto app is based on L2fwd app and it inherits
some of its parameters (such as portmask, queues per core...).

The parameter period (period of time between statistic updates)
is -T in L2fwd, but was -t in L2fwd-crypto, so for consistency,
it is changed back to -T

Fixes: 387259bd6c67 ("examples/l2fwd-crypto: add sample application")
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>