e1000: fix descriptor overflow
e1000: fix descriptor overflow

Allow rxq->rx_tail + offset > 65535
in eth_em_rx_descriptor_done().

Signed-off-by: Intel

msune/dpdk,mixja/dpdk,msune/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,msune/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,mixja/dpdk,mixja/dpdk,venkynv/dpdk-mirror,mixja/dpdk,tsphillips/dpdk-fork