linux/qemu_debug: +BRIDGE

So that veth links outgoing from two different namespaces could be
connected together.

linux/conf/qemu_debug.conf

@@ -861,7 +861,11 @@ CONFIG_IPV6_NDISC_NODETYPE=y
 # CONFIG_L2TP is not set
 CONFIG_STP=y
 CONFIG_GARP=y
-# CONFIG_BRIDGE is not set
+CONFIG_BRIDGE=y
+CONFIG_BRIDGE_IGMP_SNOOPING=y
+# CONFIG_BRIDGE_VLAN_FILTERING is not set
+# CONFIG_BRIDGE_MRP is not set
+# CONFIG_BRIDGE_CFM is not set
 # CONFIG_NET_DSA is not set
 CONFIG_VLAN_8021Q=y
 CONFIG_VLAN_8021Q_GVRP=y