(#14463) Fix to pass unit tests

(#14463) Fix to pass unit tests

* 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