bridge: new mode flag to indicate mode 'undefined'

This patch adds mode BRIDGE_MODE_UNDEF for cases where mode is not needed.
Signed-off-by: NRoopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: NScott Feldman <sfeldma@gmail.com>
Signed-off-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/uapi/linux/if_bridge.h

@@ -106,6 +106,7 @@ struct __fdb_entry {
 #define BRIDGE_MODE_VEB		0	/* Default loopback mode */
 #define BRIDGE_MODE_VEPA	1	/* 802.1Qbg defined VEPA mode */
 #define BRIDGE_MODE_SWDEV	2	/* Full switch device offload */
+#define BRIDGE_MODE_UNDEF	0xFFFF  /* mode undefined */
 
 /* Bridge management nested attributes
  * [IFLA_AF_SPEC] = {