Avert errors like this:
Parameter dport failed: Munging failed for value 1194 in class dport: can’t convert Fixnum into String

Also, pass along the protocol so Socket can make well informed decisions.

* Add default protocol to fix the test for converting a string 'ssh' to a port
number was failing like so:
  1) Puppet::Type::Firewall dport should convert a port name for dport to its number
     Failure/Error: @resource[port] = 'ssh'
     Puppet::Error:
       Parameter dport failed: Munging failed for value "ssh" in class dport: no such service ssh/proto
     # ./lib/puppet/type/../../puppet/util/firewall.rb:84:in `getservbyname'
     # ./lib/puppet/type/../../puppet/util/firewall.rb:84:in `string_to_port'
     # ./lib/puppet/type/firewall.rb:164:in `unsafe_munge'
     # ./spec/unit/puppet/type/firewall_spec.rb:161

* Always convert the response .to_s

Mostly just to get Travis to try again.