[RPC] Prefer IPv4 between IPv4 and IPv6 (apache#7013)

This change fix problem with version of IP protocol on MacOS.  Previous
the `rpc_tracker` and `query_rpc_tracker` were not able connect to each
other with default hostnames.

The root cause was in method `socket.getaddrinfo`. In `rpc_tracker` the
default hostname is "0.0.0.0" and `getaddrinfo` returns IPv4 type. In
`query_rpc_tracker` the default hastname is "localhost" and
`getaddrinfo` on MacOS returns IPv6 type. Note: on Linux both have IPv4
type.
These tools worked by different protocols and this is why
`query_rpc_tracker` wasn't able connect to `rpc_tracker`.

Now we will prefer IPv4 type. And both `rpc_tracker` and
`query_rpc_tracker` will use the same version of protocol.

python/tvm/rpc/base.py

@@ -60,6 +60,9 @@ class TrackerCode(object):
 
 def get_addr_family(addr):
     res = socket.getaddrinfo(addr[0], addr[1], 0, 0, socket.IPPROTO_TCP)
+    for info in res:
+        if info[0] == socket.AF_INET:
+            return info[0]
     return res[0][0]