can_host_socketcan_set_if allocates ifname via g_strdup, but no
instance_finalize existed to free it.
Fixes: ea15ea8a7c ("net/can: support for connecting to Linux host SocketCAN interface.")
Acked-by: Pavel Pisa <pisa@fel.cvut.cz>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>