net/ena: update version to 2.6.0

net/ena: update version to 2.6.0

This release contains multiple bug fixes and improvements, including
  - Removal of the linearization function from the xmit Tx path. The
    DPDK assumes checking for the mbuf segments number in the Tx prepare
    function.
  - Extra logs, statistics, checks...
  - Cleanup of the unused variables and definitions.
  - Configurable Link Status event.
  - Improvements for the timer service and the reset.
  - Usage of the optimized memcpy on ARM.
  - MP awareness improvements - extra API support for the secondary
    processes (like reading basic statistics).
  - Support of the xstats API to get xstat names by ID.
  - Configurable Tx completions timeout.
  - Proper setting of the meta-descriptor's DF flag.

Signed-off-by: Michal Krawczyk <mk@semihalf.com>