lldpd: Fix return value convention for "send" function.

errno values are positive values, so it's not reasonable to use E2BIG as
an error return with positive values also indicating packet lengths.

Signed-off-by: Ben Pfaff <blp@nicira.com>

lib/lldp/lldpd.c

@@ -599,7 +599,7 @@ lldpd_send(struct lldpd_hardware *hw, struct dp_packet *p)
         /* We send only if we have at least one remote system
          * speaking this protocol or if the protocol is forced */
         if (cfg->g_protocols[i].enabled > 1) {
-            if ((lldp_size = cfg->g_protocols[i].send(cfg, hw, p)) != E2BIG) {
+            if ((lldp_size = cfg->g_protocols[i].send(cfg, hw, p)) != -E2BIG) {
                 sent++;
                 continue;
             } else {