8987 bootadm: add bootfile fallback to unix

Reviewed by: Yuri Pankov <yuripv@icloud.com>
Reviewed by: C Fraire <cfraire@me.com>
Reviewed by: Andy Fiddaman <omnios@citrus-it.net>
Reviewed by: Rich Lowe <richlowe@richlowe.net>
Approved by: Dan McDonald <danmcd@joyent.com>

usr/src/cmd/boot/bootadm/bootadm_loader.c

@@ -1151,15 +1151,15 @@ update_temp(struct menu_lst *menu, char *dummy, char *opt)
 		fp = fopen(path, "w");
 		if (fp == NULL)
 			return (BAM_ERROR);
-		(void) fprintf(fp, "bootfile=\"%s\"\n", opt);
+		(void) fprintf(fp, "bootfile=\"%s;unix\"\n", opt);
 		(void) fclose(fp);
 		return (BAM_SUCCESS);
 	}
 	*o++ = '\0';
 	fp = fopen(path, "w");
 	if (fp == NULL)
 		return (BAM_ERROR);
-	(void) fprintf(fp, "bootfile=\"%s\"\n", opt);
+	(void) fprintf(fp, "bootfile=\"%s;unix\"\n", opt);
 
 	if (env != NULL) {
 		env = getenv("boot-args");