caif: Fix napi poll list corruption

The commit d75b1ade (net: less
interrupt masking in NAPI) breaks caif.

It is now required that if the entire budget is consumed when poll
returns, the napi poll_list must remain empty.  However, like some
other drivers caif tries to do a last-ditch check and if there is
more work it will call napi_schedule and then immediately process
some of this new work.  Should the entire budget be consumed while
processing such new work then we will violate the new caller
contract.

This patch fixes this by not touching any work when we reschedule
in caif.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>