ena: Update driver version to v2.6.0

Some of the changes in this release:

• Style fixes
• Fix ENI stats probing
• Add trace for the last Tx cleanup call
• Prevent LLQ initialization if member isn't exposed
• Improve logging

Obtained from: Semihalf
MFC after: 2 weeks
Sponsored by: Amazon, Inc.

(cherry picked from commit 79e1500276a993c8be857a6e32f0c05ec8f3cdc8)