- Add SRQ_BORROWING to the list of switch reasons. ULE is the only consumer

at this time.  It is used to optimize the run queue placement of threads
   who have newly elevated priorities.

sys/sys/proc.h

@@ -651,6 +651,7 @@ struct proc {
 #define SRQ_OURSELF	0x0002		/* It is ourself (from mi_switch). */
 #define SRQ_INTR	0x0004		/* It is probably urgent. */
 #define SRQ_PREEMPTED	0x0008		/* has been preempted.. be kind */
+#define	SRQ_BORROWING	0x0010		/* Priority updated due to prio_lend */
 
 /* How values for thread_single(). */
 #define	SINGLE_NO_EXIT	0