pxe: Tidy up the is_pxe global

Move this into the context to avoid a global variable. Also rename it
since the current name does not explain what it actually affects.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Artem Lapkin <email2tema@gmail.com>
Tested-by: Artem Lapkin <email2tema@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
diff --git a/cmd/sysboot.c b/cmd/sysboot.c
index 5615e81..85fa5d8 100644
--- a/cmd/sysboot.c
+++ b/cmd/sysboot.c
@@ -65,8 +65,6 @@
 	char *filename;
 	int prompt = 0;
 
-	is_pxe = false;
-
 	if (argc > 1 && strstr(argv[1], "-p")) {
 		prompt = 1;
 		argc--;
@@ -91,7 +89,7 @@
 		env_set("bootfile", filename);
 	}
 
-	pxe_setup_ctx(&ctx, cmdtp, NULL, NULL);
+	pxe_setup_ctx(&ctx, cmdtp, NULL, NULL, true);
 	if (strstr(argv[3], "ext2")) {
 		ctx.getfile = do_get_ext2;
 	} else if (strstr(argv[3], "fat")) {