rtnetlink: Honour NLM_F_ECHO flag in rtnl_newlink_create

This patch pass the netlink header message in rtnl_newlink_create() to
the new updated rtnl_configure_link(), so that the kernel could reply
unicast when userspace set NLM_F_ECHO flag to request the new created
interface info.

Suggested-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>