Factor out the common functions that will be used to initialize the
normal RX rings and the page rings.

Change the copybreak constant RX_COPY_THRESH to 128.  This same
constant will be used for the max. size of the linear SKB when pages
are used.  Copybreak will be turned off when pages are used.
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>