lib: Change frrscript_call to call function instead

lib: Change frrscript_call to call function instead

There is some rather heavy error checking logic in frrscript_call. Normally
I'd put this in the _frrscript_call function, but the error checking needs
to happen before the encoders/decoders in the macro are called.

The error checking looks messy but its really just nested ternary
expressions insite a larger statement expression.

Signed-off-by: Donald Lee <dlqs@gmx.com>