bhyve: Fix handling of -r

Just make "restore_file" a global variable so that it can be set by the
MD option handler.

Reviewed by:	corvink
Reported by:	bdrewery
Fixes:		981f9f7495 ("bhyve: Push option parsing down into bhyverun_machdep.c")
Differential Revision:	https://reviews.freebsd.org/D44974

usr.sbin/bhyve/bhyverun.c

@@ -100,6 +100,10 @@ uint16_t cpu_cores, cpu_sockets, cpu_threads;
 
 int raw_stdio = 0;
 
+#ifdef BHYVE_SNAPSHOT
+char *restore_file;
+#endif
+
 static const int BSP = 0;
 
 static cpuset_t cpumask;
@@ -656,10 +660,7 @@ main(int argc, char *argv[])
 	size_t memsize;
 	const char *value, *vmname;
 #ifdef BHYVE_SNAPSHOT
-	char *restore_file;
 	struct restore_state rstate;
-
-	restore_file = NULL;
 #endif
 
 	bhyve_init_config();

usr.sbin/bhyve/bhyverun.h

@@ -37,6 +37,10 @@
 extern int guest_ncpus;
 extern uint16_t cpu_cores, cpu_sockets, cpu_threads;
 
+#ifdef BHYVE_SNAPSHOT
+extern char *restore_file;
+#endif
+
 struct vcpu;
 struct vmctx;
 struct vm_run;