ML2 -- fixed release-specific mention
ML2 -- fixed release-specific mention

This was first implemented in 5.1, still relevant in more recent releases.

Expanded the explanation of relation between ML2 and Mellanox features.

Change-Id: I358ccdb5cdac3683efc0b82d4d1b942ba7a7ee3f

ogelbukh/fuel-docs,ogelbukh/fuel-docs,phillipsio/fuel-docs,phillipsio/fuel-docs,phillipsio/fuel-docs,stackforge/fuel-docs,phillipsio/fuel-docs,ogelbukh/fuel-docs,ogelbukh/fuel-docs,stackforge/fuel-docs