tests: fix netlink type parsing.

Netlink attribute type field is 2 bytes, not one.

MFC after:	2 weeks

tests/atf_python/sys/netlink/attrs.py

@@ -21,7 +21,7 @@ class NlAttr(object):
 
     @property
     def nla_type(self):
-        return self._nla_type & 0x3F
+        return self._nla_type & 0x3FFF
 
     @property
     def nla_len(self):

tests/atf_python/sys/netlink/message.py

@@ -205,7 +205,7 @@ class StdNetlinkMessage(BaseNetlinkMessage):
                         nla_len, len(data) - off
                     )
                 )
-            nla_type = raw_nla_type & 0x3F
+            nla_type = raw_nla_type & 0x3FFF
             if nla_type in attr_map:
                 v = attr_map[nla_type]
                 val = v["ad"].cls.from_bytes(data[off:off + nla_len], v["ad"].val)