stubdom: another for fix for lwip compile

stubdom: another for fix for lwip compile

stubdom/lwip-x86_64/src/core/dhcp.c: In function 'dhcp_create_request':
stubdom/lwip-x86_64/src/core/dhcp.c:1361:64: error: array subscript is above array bounds

The previous attempt to fix the failure above worked fine in SLE11,
openSUSE 13.1 and newer. But gcc-4.5 as included in openSUSE 11.4 still
failed to compile. To fix compilation also with this version of gcc move
the range check right into the code instead of assigning it to a
temporary variable.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>