[BUG] send_packet_out() can cause a segmentation fault if used in a transparent service

[DavideAG]

Describe the bug

send_packet_out () can cause a segmentation fault if used in a transparent service if the parent does not exist

To Reproduce

Use the tutorial 1 configuration (https://polycube.readthedocs.io/en/latest/tutorials/tutorial1/tutorial1.html)

1. create a new transparent service that uses send_packet_out
2. attach it to veth1
3. execute a ping
4. segmentation fault

Expected behavior

the service should indicate that the parent does not exist

Please tell us about your environment:

1. OS details: Ubuntu 18.04
2. Kernel details: 5.15.0-55-generic
3. Polycube Version: 0.1.0-beta+
4. Polycube Log: "Segmentation Fault"

Additional context

you need to check if the father exists.
Like

polycube/src/polycubed/src/port.cpp

Line 205 in b80ce02

logger->warn("packetout: port {0}:{1} is down", parent_.get_name(), name_);

The error is here:

polycube/src/polycubed/src/transparent_cube.cpp

Line 103 in 06f9bb4

Port *parent = dynamic_cast<Port *>(parent_);

[goldenrye]

This bug will be fixed by the commit under issue 218