lib: suppress error msg when filling the cache

Before the patch:
$ ip netns add foo
$ ip link add name veth1 address 2a:a5:5c:b9:52:89 type veth peer name veth2 address 2a:a5:5c:b9:53:90 netns foo
RTNETLINK answers: No such device
RTNETLINK answers: No such device

But the command was successful. This may break script. Let's remove those
error messages.

Fixes: 55870df ("Improve batch and dump times by caching link lookups")
Reported-by: Philippe Guibert <philippe.guibert@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

Author: NicolasDichtel

lib/ll_map.c

@@ -177,7 +177,7 @@ static int ll_link_get(const char *name, int index)
 		addattr_l(&req.n, sizeof(req), IFLA_IFNAME, name,
 			  strlen(name) + 1);
 
-	if (rtnl_talk(&rth, &req.n, &answer) < 0)
+	if (rtnl_talk_suppress_rtnl_errmsg(&rth, &req.n, &answer) < 0)
 		goto out;
 
 	/* add entry to cache */