eal: fix strnlen return value with icc

eal: fix strnlen return value with icc

The problem is that strnlen() here may return invalid value with 32bit icc.
(actually it returns it’s second parameter,e.g: sysconf(_SC_ARG_MAX)).
It starts to manifest hwen max_len parameter is > 2M and using icc –m32 –O2 (or above).

Suggested-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Signed-off-by: Cunming Liang <cunming.liang@intel.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>