net/qede: fix Rx buffer size calculation

net/qede: fix Rx buffer size calculation

 - HW does not include CRC in received frame when passed to host,
   so no need to consider CRC length while calculating Rx buffer size.
 - In scattered Rx mode, driver may allocate Rx buffer larger than
   the size of mbuf because it tries to adjust the buffer size to cache
   line size by ceiling it. Fix this by flooring the size instead of
   ceiling.
 - Consider the rule imposed by HW regarding the minimum size of Rx buffer
   in scattered Rx mode -
   (MTU + Maximum L2 Header Size + 2) / ETH_RX_MAX_BUFF_PER_PKT

Fixes: f6033f2497e7 ("net/qede: fix minimum buffer size and scatter Rx check")
CC: stable@dpdk.org
Signed-off-by: Shahed Shaikh <shahed.shaikh@cavium.com>