net: extend net_device allocation to vmalloc()

net: extend net_device allocation to vmalloc()

Joby Poriyath provided a xen-netback patch to reduce the size of
xenvif structure as some netdev allocation could fail under
memory pressure/fragmentation.

This patch is handling the problem at the core level, allowing
any netdev structures to use vmalloc() if kmalloc() failed.

As vmalloc() adds overhead on a critical network path, add __GFP_REPEAT
to kzalloc() flags to do this fallback only when really needed.

Signed-off-by: Eric Dumazet <[email protected]>
Reported-by: Joby Poriyath <[email protected]>
Cc: Ben Hutchings <[email protected]>
Signed-off-by: David S. Miller <[email protected]>