Driver's NAPI poll is using a long sequence for processing ingress
packets, and it's going to get even longer once we do XDP.
Break down the main loop into a series of sub-functions to allow
better readability of the function.

While we're at it, correct the accounting of the NAPI budget -
currently we're counting only packets passed to the stack against
the budget, even in case those are actually aggregations.
After refactoring every CQE processed would be counted against the budget.
Signed-off-by: Yuval Mintz <Yuval.Mintz@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>