Functions correction. Testing.
Output for tested functions:
['tcp.srcport', 'tcp.dstport', 'tcp.flags']
['ip.src', 'ip.dst', 'ip.ttl']
['udp.srcport', 'udp.dstport']
['icmp.code', 'icmp.type']
['frame.number', 'frame.time_epoch', 'frame.len']
['dns.qry.name', 'dns.qry.type', 'dns.a', 'dns.ptr.domain_name']

Parsing of ip, tcp, udp, icmp, dns, frame protocols - successfull.