Preserve bridge MTU in KVM ifup script

Closes: #201 - KVM_IFUP does not set bridge-MTU on tap devices
Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>
(cherry picked from commit a1ec8695)

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

tools/kvm-ifup.in

@@ -36,6 +36,8 @@ fi
 ip link set $INTERFACE up
 
 if [ "$MODE" = "bridged" ]; then
+	ip link set $INTERFACE mtu $(</sys/class/net/${BRIDGE}/mtu)
+
 	# Connect the interface to the bridge
 	brctl addif $BRIDGE $INTERFACE
 else