def is?(protocol)
      klass = check_protocol protocol
      headers.any? { |h| h.is_a? klass }
    end
def is?(protocol)
      klass = check_protocol protocol
      headers.any? { |h| h.is_a? klass }
    end
Check if a protocol header is embedded in packet.
   pkt = PacketGen.gen('IP').add('UDP')
   pkt.is?('IP')   #=> true
   pkt.is?('TCP')  #=> false
 @return [Boolean]
 @raise [ArgumentError] unknown protocol