Updated FreeBSD rtl81xx network driver with the 10.0 release.

Should fix #10412.

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
ByteOrder.h: simplify compiler test

* A problem with our gcc requires adding casts for gcc4 when
  the __builtin_bswap functions are used with a format string
* Unlike gcc2, the __builtin_bswap functions do not get disabled
  despite using -fno-builtins, hence added compiler check in
  runtime_loader/utility.cpp