frr: T6746: add guard time after cli_commit() and before getFRRconfig()

As vyos-configd will take care about the commit via FRRender class, and FRR
needs to internally process the configuration we might read it back via vtysh
"to fast". Add a 5 seconds guard timer after each cli_commit() and before
calling getFRRconfig().

Guard timer is reset every time, cli_commit() is called.