cxgbe(4): Overhaul CLIP (Compressed Local IPv6) table management.

• Process the list of local IPs once instead of once per adapter. Add addresses from all VNETs to the driver's list but leave hardware updates for later when the global VNET/IFADDR list locks have been released.

• Add address to the hardware table synchronously when a CLIP entry is requested for an address that's not already in there.

• Provide ioctls that allow userspace tools to manage addresses in the CLIP table.

• Add a knob (hw.cxgbe.clip_db_auto) that controls whether local IPs are automatically added to the CLIP table or not.

Sponsored by: Chelsio Communications

(cherry picked from commit 24b98f288d11750f2cdfbfe360be1c92a9c2ee1d)