The SR-IOV agent support l2 agent extension due to
this patch https://review.openstack.org/#/c/210483/
This patch allow to show the loaded l2 agent extensions
when executing neutron agent-show <SR-IOV agent id>
Closes-Bug: #1527307
DocImpact update the agent configuration to show
l2 agent extensions
Change-Id: I5dcb79ef539e4f18693e4a8eff03fff40873d3fa