Fix spec-bug-induced bug in finding the !PXE structure if PXENV+ was found.
Starting with 1.47, changes marked with SYSLINUX/PXELINUX apply to
that specific program only; other changes apply to both.
+Changes in 1.54:
+ * PXELINUX: Fix code for finding !PXE from PXENV+. This was
+ due to a spec bug; match the most recent spec since that
+ seems to be what implementations actually do.
+
Changes in 1.53:
* PXELINUX: Rename pxelinux.bin to pxelinux.0, to match what
most PXE servers seem to expect.
jb old_api
mov si,bx
mov ax,es
- les bx,[es:bx+26h] ; !PXE structure pointer
+ les bx,[es:bx+28h] ; !PXE structure pointer
cmp dword [es:bx],'!PXE'
je have_pxe