Using power of 2 descriptors number makes the ring management easier
and allows to use mask operation instead of wraparound conditions.
Adjust Tx descriptor number to be power of 2 and change calculation to
use mask accordingly.
Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
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