nyoci_outbound_append_content_formatted sets incorrect length

[snej]

In nyoci_outbound_append_content_formatted(), the variable fmtlen is updated but unused:

    fmtlen += self->outbound.content_len;
    ret = nyoci_outbound_set_content_len((coap_size_t)len);
bail:
    va_end(args);
    return ret;
}

/Couchbase/Embedded/libnyoci/src/libnyoci/nyoci-outbound.c:647:2: warning: Value stored to 'fmtlen' is never read
        fmtlen += self->outbound.content_len;
        ^         ~~~~~~~~~~~~~~~~~~~~~~~~~~

I was going to ignore this compiler warning, but then I looked at the code, and it seems like the parameter to nyoci_outbound_set_content_len() should be fmtlen, not len -- the latter is just the space remaining in the packet, while fmtlen is the previous content_len plus the number of bytes written by vsnprintf.

[darconeous]

Good catch!