NetworkPkg: Correct the DNS token return status by RCODE

When HostNameToIp() and GeneralLookUp() are called with a invalid
host name, RCODE (4 bit field is set as part of responses) error
will returned in packet to identify the domain name referenced in
the query does not exist. So, EFI_NOT_FOUND should be returned
directly.

Current implementation only check the RCODE in successful condition.
Need update the code for more error check according to RFC 1035 4.1.1
section.

Cc: Hegde Nagaraj P <nagaraj-p.hegde@hpe.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Tested-by: Hegde Nagaraj P <nagaraj-p.hegde@hpe.com>
Reviewed-by: Sriram Subramanian <sriram-s@hpe.com>