IPACM: fix ipv6 ecm-backhaul issue

In ecm-backhaul use case, IPv6 address assignment
on MDM is failing in USB cradle mode. The fix is
to check wan instance is in LTE mode or STA mode.

Change-Id: I94c1628f12f9c12437d2d76455ad3044753bcf92
diff --git a/ipacm/src/IPACM_Wan.cpp b/ipacm/src/IPACM_Wan.cpp
index d45bad2..fd724cb 100644
--- a/ipacm/src/IPACM_Wan.cpp
+++ b/ipacm/src/IPACM_Wan.cpp
@@ -204,7 +204,7 @@
 
         if (num_dft_rt_v6 == 0)
 	    {
-			if(m_is_sta_mode == m_is_sta_mode)
+			if(m_is_sta_mode == Q6_WAN)
 			{
 				modem_ipv6_pdn_index = num_ipv6_modem_pdn;
 				num_ipv6_modem_pdn++;
@@ -258,7 +258,7 @@
         IPACMDBG("ipv4 wan iface rt-rule hdll=0x%x\n", dft_rt_rule_hdl[0]);
 			/* initial multicast/broadcast/fragment filter rule */
 
-		if(m_is_sta_mode == m_is_sta_mode)
+		if(m_is_sta_mode == Q6_WAN)
 		{
 			modem_ipv4_pdn_index = num_ipv4_modem_pdn;
 			num_ipv4_modem_pdn++;