tools: Update endian definitions for Mac OSX

tools: Update endian definitions for Mac OSX

  - it appears (at least from OS X verison 10.10, Yosemite) that the
    big and little endian defintions have changed.

    the older

       #include <sys/_endian.h>
       #include <architecture/byte_order.h>

    reference yielded the following warning:

         #define __bswap_16(x)      NXSwapShort(x)
                                    ^
       /usr/include/architecture/byte_order.h:45:1: note: 'NXSwapShort' has been explicitly marked deprecated here

    For the new OS X editions, it seems that we need to refer to:

      #include <netinet/in.h>
      #include <libkern/OSByteOrder.h>

    and respectively use 'OSSwapInt16', 'OSSwapInt32', & 'OSSwapInt64', in
    place of 'NXSwapShort', 'NXSwapLong' & 'NXSwapLongLong'.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>