examples/exception_path: limit core count to 64
examples/exception_path: limit core count to 64

Application doesn't support more that 64 lcores due to command
line limitation of using a coremask that is parsed as a 64bit
value, so changed it to reflect this limitation.

Coverity issue: 30688
Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Radu Nicolau <fa459cf59d47c122ba776e9a6f631c862bf44680@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk