resolved: be more careful with types in dns_stream_writev()

resolved: be more careful with types in dns_stream_writev()

Let's not name a variable of type ssize_t "r". We usually use "r" for
return values of API calls that return some kind of error as in int.
This creates a lot of confusion if used differently here, which actually
resulted in connect()'s return value being assigned to this mistyped "r"
by accident.

Let's rename the variable "m" hence, and not use it for connect() return
values.