First dividing by interval before multiplying with 1000 decreases the
precision by +-(interval - 1) * 1000, as interval arithmetic always
applies the Gauß-function to the result.

This is not necessary and simply reordering the operations mitigates
this.

Within the components, snprintf() was unchecked and had inefficient
calls in some places.
We implement esnprintf() that does all the dirty laundry for us
and use it exclusively now.

implemented additional error condition for openbsd netstat in case the
interface could not be found in the interface list or if_data is not
readable.

implemented the netspeed functionality for openbsd.
furthermore the static keyword was removed of the interval variable in
config.def.h for usage as extern variable.