Merge branch 'net-smc-fixes'

Karsten Graul says:

====================
net/smc: fixes 2020-07-16

Please apply the following patch series for smc to netdev's net tree.

The patches address problems caused by late or unexpected link layer
control packets, dma sync calls for unmapped memory, freed buffers
that are not removed from the buffer list and a possible null pointer
access that results in a crash.

v1->v2: in patch 4, improve patch description and correct the comment
        for the new mutex
====================

Signed-off-by: David S. Miller <davem@davemloft.net>