e1000: Don't enable polling in open() (was: e1000: assertion hit in e1000_clean(), kernel 2.6.21.1)

Herbert Xu wrote:
"netif_poll_enable can only be called if you've previously called
netif_poll_disable.  Otherwise a poll might already be in action
and you may get a crash like this."

Removing the call to netif_poll_enable in e1000_open should fix this issue,
the only other call to netif_poll_enable is in e1000_up() which is only
reached after a device reset or resume.

Bugzilla: http://bugzilla.kernel.org/show_bug.cgi?id=8455
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=240339

Tested by Doug Chapman <doug.chapman@hp.com>

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jeff Garzik <jeff@garzik.org>