Support 64bit limit for police actions

[jfogh-akamai]

The issue

The library currently only supports 32 bit values for "rate" and "peak rate" in police actions.

Implementation notes

The fields are stored in the struct nl.TcPolice, which only supports 32 bits. The protocol supports separate 64bit attributes, which can be appended after the nl.TcPolice instance.

This change is completely analogous to the commit "implemented handling of uint64 for HTB class rate/ceil
".

NB:
I expect to have a PR ready within a few days.

[aboch]

Thank you