nl_vxlan::create_endpoint(): fix error log on add neigh failure

There is no link variable in this nl_vxlan::create_endpoint(), only
vxlan_link and br_link. This was hidden due to the OBJ_CAST(), but when
the OBJ_CAST() was dropped, g++ started to complain.

Fix this by replacing link with neigh, since neigh is what the text
before the variable says.

Fixes the following warning:

../git/src/netlink/nl_vxlan.cc: In member function 'int basebox::nl_vxlan::create_endpoint(rtnl_link*, rtnl_link*, nl_addr*)':
../git/src/netlink/nl_vxlan.cc:674:45: warning: the address of 'int link(const char*, const char*)' will never be NULL [-Waddress]
  674 |                  << ") to add l2 neigh " << link;
      |                                             ^~~~

Fixes: ec04fe2 ("vxlan: add existing neighbors for new endpoint")
Signed-off-by: Jonas Gorski <[email protected]>

src/netlink/nl_vxlan.cc

@@ -671,7 +671,7 @@ int nl_vxlan::create_endpoint(rtnl_link *vxlan_link, rtnl_link *br_link,
     rv = add_l2_neigh(neigh, lport_id, tunnel_id);
     if (rv < 0) {
       LOG(ERROR) << __FUNCTION__ << ": failed (rv=" << rv
-                 << ") to add l2 neigh " << link;
+                 << ") to add l2 neigh " << neigh;
     }
   }