Update to the latest version of iPXE

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

diff --git a/ipxe b/ipxe
index 300a371bfbfee4b84e413ffc5cf800ee8f79a4fd..1b67a0564657b6fcef18b1588ea6491ca1b1996d 160000 (submodule)
--- a/ipxe
+++ b/ipxe
@@ -1 +1 @@
-Subproject commit 300a371bfbfee4b84e413ffc5cf800ee8f79a4fd
+Subproject commit 1b67a0564657b6fcef18b1588ea6491ca1b1996d