net/dns.c: Fix endian conversion for big-endian in dns command

net/dns.c used endian conversion macros wrongly (shorts in reply
were put swapped into CPU, and then ntohs() was used to swap it
back, which broke on big-endian).

Fix this by using the correct linux conversion macro for reading
a unaligned short in network byte order: get_unaligned_be16()
Thanks to Mike Frysinger pointing at the best macro to use.

Tested on big and little endian qemu boards (mips and versatile)

Signed-off-by: Bernhard Kaindl <bernhard.kaindl@thalesgroup.com>
Cc: Pieter Voorthuijsen <pieter.voorthuijsen@prodrive.nl>
Cc: Robin Getz <rgetz@blackfin.uclinux.org>
Acked-by: Mike Frysinger <vapier@gentoo.org>