fix service port number lookup to use protocol

fix service port number lookup to use protocol

The existing code passes `:proto`, which `string_to_port` casts to a
string, gets "proto", compares that to the possibilities "udp" or "tcp",
and when neither, falls back to using "tcp".

This patch passes the actual proto value to the function, in case there is
a UDP specific service in your /etc/services (uncommon, but it happens).
It looks like Puppet will evaluate the properties in declared order,
so I had to move `newproperty(:proto)` up so `@resource[:proto]` was
available in the code for `sport`, `dport` and `port`.