octeon_ep: Implement helper for iterating packets in Rx queue

[ Upstream commit bd28df26 ]

The common code with some packet and index manipulations is extracted and
moved to newly implemented helper to make the code more readable and avoid
duplication. This is a preparation for skb allocation failure handling.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Suggested-by: Simon Horman <horms@kernel.org>
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Stable-dep-of: eb592008 ("octeon_ep: Add SKB allocation failures handling in __octep_oq_process_rx()")
Signed-off-by: Sasha Levin <sashal@kernel.org>