be2net: fix bug in rx page posting

Pages are posted to the rxq in such a way that more than one frag
can share the page. The last frag that uses the page unmaps the
page.  In the case when a page is not fully used (due to lack of space in rxq)
the last frag that uses the page is not being set as a "last_page_user";
instead, the next frag in the rxq is incorrectly being set.

The fix has also been tested on ppc64 with 64k pages...

Signed-off-by: Sathya Perla <sathyap@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>