ruby: slicc: use default argument value

ruby: slicc: use default argument value
Before this patch, while one could declare / define a function with default
argument values, but the actual function call would require one to specify
all the arguments.  This patch changes the check for  function arguments.
Now a function call needs to specify arguments that are at least as much as
those with default values and at most the total number of arguments taken
as input by the function.