[qca-nss-ecm]: multicast: fix for crash in ecm while rebooting with traffic running

Description: DUT crash when try to deref an invalid interface hierarchy while
	     creating destination interface heirarchies

Change-Id: I2b737be2547e18792508ca51f22749984ad0475f
Signed-off-by: Shyam Sunder <ssunde@codeaurora.org>
diff --git a/ecm_interface.c b/ecm_interface.c
index 88c7c0c..87e7450 100644
--- a/ecm_interface.c
+++ b/ecm_interface.c
@@ -1878,7 +1878,7 @@
 	uint32_t *interface_first;
 	uint32_t br_if;
 	uint32_t valid_if;
-        uint32_t if_num;
+	int32_t if_num;
 	int32_t dest_dev_type;
 	int if_index;
 	int ii_cnt;
@@ -1965,6 +1965,11 @@
 				if_num = mc_bridge_ipv6_get_if(dest_dev, &origin6, &group6, mc_max_dst, mc_dst_if_index);
 			}
 
+			if ((if_num <= 0) || (if_num > ECM_DB_MULTICAST_IF_MAX)) {
+				dev_put(dest_dev);
+				return 0;
+			}
+
 			for (br_if = 0; br_if < if_num; br_if++) {
 				mc_br_slave_dev = dev_get_by_index(&init_net, mc_dst_if_index[br_if]);
 				if (!mc_br_slave_dev) {