NetworkPkg/DnsDxe: [CVE-2018-12178] Check the received packet size before parsing...

NetworkPkg/DnsDxe: [CVE-2018-12178] Check the received packet size before parsing the message.

Fix CVE-2018-12178
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=809

The DNS driver only checks the received packet size against the
minimum DNS header size in DnsOnPacketReceived(), later it accesses
the QueryName and QuerySection beyond the header scope, which might
cause the pointer within DNS driver points to an invalid entry or
modifies the memory content beyond the header scope.

This patch is to fix above problem.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wang Fan <fan.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>