iflib: Add new shared flag: IFLIB_ADMIN_ALWAYS_RUN

ixl(4)'s nvmupdate utility expects the nvmupdate process to run
while the interface is down; these nvm update commands use the
admin queue, so the admin queue needs to be able to generate
interrupts and be processed while the interface is down.

So add a flag that ixl(4) sets that lets the entire admin task
run even when the interface is marked down/IFF_DRV_RUNNING isn't set.

With this change, nvmupdate should function like it did pre-iflib.

Reviewed by:	gallatin@, sbruno@
MFC after:	1 week
Sponsored by:	Intel Corporation
Differential Revision:	https://reviews.freebsd.org/D15575

sys/net/iflib.c

@@ -3807,7 +3807,8 @@ _task_fn_admin(void *context)
 	ctx->ifc_flags &= ~(IFC_DO_RESET|IFC_DO_WATCHDOG);
 	STATE_UNLOCK(ctx);
 
-	if (!running & !oactive)
+	if ((!running & !oactive) &&
+	    !(ctx->ifc_sctx->isc_flags & IFLIB_ADMIN_ALWAYS_RUN))
 		return;
 
 	CTX_LOCK(ctx);

sys/net/iflib.h

@@ -358,7 +358,10 @@ typedef enum {
  * autogenerate a MAC address
  */
 #define IFLIB_GEN_MAC	0x08000
-
+/*
+ * Interface needs admin task to ignore interface up/down status
+ */
+#define IFLIB_ADMIN_ALWAYS_RUN	0x10000
 
 
 /*