test: check zero socket memory as valid

test: check zero socket memory as valid

Dynamic memory mode allowes zero socket-mem because all the
required memory could be allocated on demand.

Fixes: 0a703f0f36c1 ("eal/linux: fix parsing zero socket memory and limits")
Cc: stable@dpdk.org
Reported-by: Shuai Zhu <shuaix.zhu@intel.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>