Flow expiry: Add a send_flow_exp flag to the sw_flow struct

This flag is used to indicate whether a flow expiry should be sent to
the controller.

datapath/flow.h

@@ -91,6 +91,7 @@ struct sw_flow {
 	uint16_t idle_timeout;	/* Idle time before discarding (seconds). */
 	uint16_t hard_timeout;  /* Hard expiration time (seconds) */
 	uint64_t used;          /* Last used time (in jiffies). */
+        uint8_t send_flow_exp;  /* Send a flow expiry to the controller */
 
 	struct sw_flow_actions *sf_acts;
 

udatapath/switch-flow.h

@@ -65,6 +65,7 @@ struct sw_flow {
     uint64_t packet_count;      /* Number of packets seen. */
     uint64_t byte_count;        /* Number of bytes seen. */
     uint8_t reason;             /* Reason flow expired (one of NXFER_*). */
+    uint8_t send_flow_exp;      /* Send a flow expiry to the controller */
 
     uint8_t tcp_flags;          /* Union of seen TCP flags. */
     uint8_t ip_tos;             /* IP TOS value. */