Suppress irrelevant gcc warning (mpls).

Modern gcc can warn about MPLS array accessed above its defined size
(which is MPLS_DEPTH) in Elements switch:

  warning: array subscript is above array bounds [-Warray-bounds]

Disabling this warning is safe, because, these statements only called
for a valid array length (due to template definition is based on
MPLS_DEPTH), so, supposedly over-reading code is never called.
For a double safety, sanity checking is added for --promisc-mpls value
(which defines MPLS_DEPTH) to be in range of 1..10.

configure

@@ -305,7 +305,7 @@ do
     --enable-sampl*) KOPTS="$KOPTS -DENABLE_SAMPLER" ;;
     --enable-aggr*)  KOPTS="$KOPTS -DENABLE_AGGR" ;;
     --enable-promi*)   ENABLE_PROMISC=1 ;;
-    --promisc-mpls*)   ENABLE_PROMISC=1; PROMISC_MPLS=1; MPLS_DEPTH="$ac_optarg" ;;
+    --promisc-mpls*)   ENABLE_PROMISC=1; PROMISC_MPLS=1; MPLS_DEPTH=${ac_optarg:-3} ;;
     --enable-snmp-r*)  KOPTS="$KOPTS -DENABLE_SNMP" ;;
     --enable-physdev)       KOPTS="$KOPTS -DENABLE_PHYSDEV" ;;
     --enable-physdev-over*) KOPTS="$KOPTS -DENABLE_PHYSDEV_OVER" ;;
@@ -324,11 +324,12 @@ done
 if [ "$ENABLE_PROMISC" = 1 ]; then KOPTS="$KOPTS -DENABLE_PROMISC"; fi
 if [ "$PROMISC_MPLS" = 1 ]; then
   KOPTS="$KOPTS -DPROMISC_MPLS"
-  if [ "$MPLS_DEPTH" -gt 10 ]; then
+  case "$MPLS_DEPTH" in (*[!0-9]*|"") MPLS_DEPTH=1 ;; esac
+  if [ "$MPLS_DEPTH" -lt 1 ]; then
+    echo "! Requested MPLS stack depth is too small, limiting to 1."
+  elif [ "$MPLS_DEPTH" -gt 10 ]; then
     echo "! Requested MPLS stack depth is too big, limiting to 10."
     MPLS_DEPTH=10;
-  elif [ ! "$MPLS_DEPTH" ]; then
-    MPLS_DEPTH=3
   fi
   if [ "$MPLS_DEPTH" -ge 1 ]; then KOPTS="$KOPTS -DMPLS_DEPTH=$MPLS_DEPTH"; fi
 fi

ipt_NETFLOW.c

@@ -3463,6 +3463,8 @@ static inline void add_tpl_field(__u8 *ptr, const int type, const struct ipt_net
 	case sourceMacAddress:	    memcpy(ptr, &nf->tuple.h_src, ETH_ALEN); break;
 #endif
 #ifdef MPLS_DEPTH
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Warray-bounds"
 	case MPLS_LABEL_1:    memcpy(ptr, &nf->tuple.mpls[0], 3); break;
 	case MPLS_LABEL_2:    memcpy(ptr, &nf->tuple.mpls[1], 3); break;
 	case MPLS_LABEL_3:    memcpy(ptr, &nf->tuple.mpls[2], 3); break;
@@ -3475,6 +3477,7 @@ static inline void add_tpl_field(__u8 *ptr, const int type, const struct ipt_net
 	case MPLS_LABEL_9:    memcpy(ptr, &nf->tuple.mpls[8], 3); break;
 	case MPLS_LABEL_10:   memcpy(ptr, &nf->tuple.mpls[9], 3); break;
 # endif
+# pragma GCC diagnostic pop
 	case mplsTopLabelTTL: *ptr = ntohl(nf->tuple.mpls[0]); break;
 #endif
 #ifdef ENABLE_DIRECTION
@@ -5413,6 +5416,9 @@ static int __init ipt_netflow_init(void)
 	}
 
 #ifdef MPLS_DEPTH
+	/* template_mpls is terminated on the MPLS_DEPTH mark, so, it
+	 * never send Element which can access mpls labels array above
+	 * its defined MPLS_DEPTH value. */
 	if (MPLS_DEPTH >= 0 && MPLS_DEPTH < 10)
 		template_mpls.types[MPLS_LABELS_BASE_INDEX + MPLS_DEPTH] = 0;
 #endif