[vnetorch] [vxlanorch] fix a set of memory usage issues (#2352)

* [vnetorch] fix use-after-free in removeBfdSession()
* using a copy of monitor ip instead of a reference since the reference gets invalidated after the endpoint is erased

Signed-off-by: Yakiv Huryk <yhuryk@nvidia.com>

Author: Yakiv-Huryk

orchagent/vnetorch.cpp

@@ -1602,7 +1602,8 @@ void VNetRouteOrch::delEndpointMonitor(const string& vnet, NextHopGroupKey& next
         if (nexthop_info_[vnet].find(ip) != nexthop_info_[vnet].end()) {
             if (--nexthop_info_[vnet][ip].ref_count == 0)
             {
-                removeBfdSession(vnet, nhk, nexthop_info_[vnet][ip].monitor_addr);
+                IpAddress monitor_addr = nexthop_info_[vnet][ip].monitor_addr;
+                removeBfdSession(vnet, nhk, monitor_addr);
             }
         }
     }

orchagent/vxlanorch.cpp

@@ -1110,13 +1110,14 @@ void VxlanTunnel::updateRemoteEndPointIpRef(const std::string remote_vtep, bool
             it->second.ip_refcnt++;
         }
         SWSS_LOG_DEBUG("Incrementing remote end point %s reference to %d", remote_vtep.c_str(),
-                       it->second.ip_refcnt);
+                       tnl_users_[remote_vtep].ip_refcnt);
     }
     else
     {
         if (it == tnl_users_.end())
         {
             SWSS_LOG_ERROR("Cannot decrement ref. End point not referenced %s", remote_vtep.c_str());
+            return;
         }
         it->second.ip_refcnt--;