examples/l3fwd-power: fix updating lcore parameters

examples/l3fwd-power: fix updating lcore parameters

When perf-config option is specified, we are calling into the power
library even though it may not necessarily be enabled. It is
questionable whether perf-config option is even applicable to non-power
library modes, but for now, fix it just by avoiding calling into the
power library if it wasn't initialized, and assume that every lcore is
high performance core.

Fixes: e0194feb322c ("examples/l3fwd-power: add interrupt-only mode")
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: David Hunt <david.hunt@intel.com>