Check that THP is not set to always (madvise is ok) (#4001)

THP can also be set to madvise, in which case it shouldn't cause
problems for Redis since redis (or the allocator) doesn't use madvise
to activate it.

src/latency.c

@@ -71,7 +71,7 @@ int THPIsEnabled(void) {
         return 0;
     }
     fclose(fp);
-    return (strstr(buf,"[never]") == NULL) ? 1 : 0;
+    return (strstr(buf,"[always]") != NULL) ? 1 : 0;
 }
 #endif