epc,gtpu: log info when IPv6 packet is sent

we've logged in warning mode bc we don't support IPv6 but its
causing unwanted noise in the epc log file.

it's quite normal that the Linux network stack sends IPv6 router
solicitation packets, etc. So we just ignore them and that's it.

srsepc/src/mbms-gw/mbms-gw.cc

@@ -273,7 +273,7 @@ void mbms_gw::handle_sgi_md_pdu(srslte::byte_buffer_t* msg)
   // IP Headers
   struct iphdr* iph = (struct iphdr*)msg->msg;
   if (iph->version != 4) {
-    m_mbms_gw_log->warning("IPv6 not supported yet.\n");
+    m_mbms_gw_log->info("IPv6 not supported yet.\n");
     return;
   }
 

srsepc/src/spgw/gtpu.cc

@@ -199,7 +199,7 @@ void spgw::gtpu::handle_sgi_pdu(srslte::byte_buffer_t* msg)
   m_gtpu_log->debug("Received SGi PDU. Bytes %d\n", msg->N_bytes);
 
   if (iph->version != 4) {
-    m_gtpu_log->warning("IPv6 not supported yet.\n");
+    m_gtpu_log->info("IPv6 not supported yet.\n");
     return;
   }
   if (ntohs(iph->tot_len) < 20) {