Port splitting and breakout cable support

Ports default to an unsplit state. When a port is 'split', the split interfaces become active and can be configured independently. For example, when a 40G QSFP+ port is split four ways, each split interface behaves like a separate 10G SFP+ port. The split interfaces have the same name as the base port with an added suffix to represent their lane of the breakout cable. Splitting an interface removes most of the port's configuration settings and makes it inactive. The port will no longer appear in many show interface commands and most configuration commands are not allowed.

The same thing happens in reverse when an interface is unsplit. However, note that the 'split' and 'no split' commands are always performed in the unsplit port's context. After splitting a port, a reboot is required to complete the process. On a chassis system, just the line modules of all newly split ports can be rebooted Otherwise, the entire system must be rebooted. Until the reboot, split interfaces can continue to be configured, but will remain in a 'down' state.