This change introduces new sysctl handlers that allow the user to change RX/TX ring sizes. As before, the default ring sizes will come from the device (usually 1024). We also get the max/min limits from the device. In the case min values are not provided we have statically defined constants for the min values. Additionally, if the modify ring option is not enabled on the device, changing ring sizes via sysctl will not be possible. When changing ring sizes, the interface turns down momentarily while allocating/freeing resources as necessary.

Signed-off-by: Vee Agarwal <veethebee@google.com>