Merge branch 'net-Fix-bridge-enslavement-failure'

Ido Schimmel says:

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net: Fix bridge enslavement failure

Patch #1 fixes an issue in which an upper netdev cannot be enslaved to a
bridge when it has multiple netdevs with different parent identifiers
beneath it.

Patch #2 adds a test case using two netdevsim instances.
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Signed-off-by: David S. Miller <davem@davemloft.net>