virnetlink: fix build error

Commint 0473b45c introduced new function virNetlinkDelLink, but in
it's counterpart for non-linux platform there should be ATTRIBUTE_UNUSED
instead of ATTRIBUTE_UNSUPPORTED.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

src/util/virnetlink.c

@@ -886,7 +886,7 @@ int virNetlinkCommand(struct nl_msg *nl_msg ATTRIBUTE_UNUSED,
 
 
 int
-virNetlinkDelLink(const char *ifname ATTRIBUTE_UNSUPPORTED)
+virNetlinkDelLink(const char *ifname ATTRIBUTE_UNUSED)
 {
     virReportError(VIR_ERR_INTERNAL_ERROR, "%s", _(unsupported));
     return -1;