Function SCIPchgCapacityKnapsack 

pub unsafe extern "C" fn SCIPchgCapacityKnapsack(
    scip: *mut SCIP,
    cons: *mut SCIP_CONS,
    capacity: c_longlong,
) -> SCIP_RETCODE

changes capacity of the knapsack constraint

@note This method can only be called during problem creation stage (SCIP_STAGE_PROBLEM)