Merge branch 'rtnetlink-allow-to-enslave-with-one-msg-an-up-interface'

Nicolas Dichtel says:

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rtnetlink: allow to enslave with one msg an up interface

The first patch fixes a regression, introduced in linux v6.1, by reverting
a patch. The second patch adds a test to verify this API.
====================

Link: https://lore.kernel.org/r/20240108094103.2001224-1-nicolas.dichtel@6wind.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>