[IPX]: Another nonlinear receive fix

Need to check some more cases in IPX receive.  If the skb is purely
fragments, the IPX header needs to be extracted. The function
pskb_may_pull() may in theory invalidate all the pointers in the skb,
so references to ipx header must be refreshed.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>