net_dma: simple removal

net_dma: simple removal

Per commit "77873803363c net_dma: mark broken" net_dma is no longer used
and there is no plan to fix it.

This is the mechanical removal of bits in CONFIG_NET_DMA ifdef guards.
Reverting the remainder of the net_dma induced changes is deferred to
subsequent patches.

Marked for stable due to Roman's report of a memory leak in
dma_pin_iovec_pages():

    https://lkml.org/lkml/2014/9/3/177

Cc: Dave Jiang <[email protected]>
Cc: Vinod Koul <[email protected]>
Cc: David Whipple <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: <[email protected]>
Reported-by: Roman Gushchin <[email protected]>
Acked-by: David S. Miller <[email protected]>
Signed-off-by: Dan Williams <[email protected]>