net/mlx4: merge Tx queue rings management

net/mlx4: merge Tx queue rings management

The Tx queue send ring was managed by Tx block head,tail,count and mask
management variables which were used for managing the send queue remain
space and next places of empty or completed work queue entries.

This method suffered from an actual addresses recalculation per packet,
an unnecessary Tx block based calculations and an expensive dual
management of Tx rings.

Move send queue ring calculation to be based on actual addresses while
managing it by descriptors ring indexes.

Add new work queue entry pointer to the descriptor element to hold the
appropriate entry in the send queue.

Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>