The CEF switching State for the interface.
If CEF is enabled but distributed CEF(dCEF) is
disabled then CEF is in cefEnabled(1) state.
If distributed CEF is enabled, then CEF is in
distCefEnabled(2) state. The cefDisabled(3) state
indicates that CEF is disabled.
The CEF switching state is only applicable to the
received packet on the interface.