[ECOS] To diable bootp.

[Park Jun-Ku]

I want to disable bootp.
So, disabled options that "Do not try to use BOOTP".

And it did generate
    #define CYGSEM_REDBOOT_DEFAULT_NO_BOOTP 1

But, code in redboot/src/net_io.c says that
#ifdef CYGSEM_REDBOOT_DEFAULT_NO_BOOTP
    use_bootp = CYGSEM_REDBOOT_DEFAULT_NO_BOOTP;
#else
    use_bootp = true;
#endif

And the code says that always use bootp.

So, I modified the code.
    use_bootp = !CYGSEM_REDBOOT_DEFAULT_NO_BOOTP;

Did I correctly modify it ?