QDnsLookup: Fix build with uClibc

uClibc doesn't have a nsmap member in __res_state. Since it also doesn't have
res_nquery() which is mandatory for QDnsLookup, we can simply disable the code
to fix the build.

Change-Id: Ia872f535519aca3a2de763548c6dd0e3e0ee20d4
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Reviewed-by: Mandeep Sandhu <mandeepsandhu.chd@gmail.com>