Workaround to allow snc4+cache but reject other snc4 configurations

I've created this patch which we're using in-house to allow snc4+cache and reject other snc4 combinations.

src/plugins/node_features/knl_cray/node_features_knl_cray.c

@@ -1779,6 +1779,18 @@ extern int node_features_p_job_valid(char *job_features)
 	if (numa_cnt > 1)			/* Multiple NUMA options */
 		return ESLURM_INVALID_KNL;
 
+	/* snc4 only allowed with cache today due to invalid config information
+	 * reported by kernel to hwloc, then to Slurm */
+	if (!job_numa) {
+	    job_numa = default_numa;
+	}
+	if (!job_mcdram) {
+	    job_mcdram = default_mcdram;
+	}
+	if (job_numa == KNL_SNC4 && job_mcdram != KNL_CACHE) {
+		return ESLURM_INVALID_KNL;
+	}
+
 	return SLURM_SUCCESS;
 }