sh_eth: place RX/TX descriptor *enum*s after their *struct*s

Place the RX/TX descriptor bit *enum*s where they belong -- after the
corresponding RX/TX descriptor *struct*s and, while at it, switch to
declaring one *enum* entry per line...

Signed-off-by: Sergey Shtylyov <s.shtylyov@omprussia.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>