babeld: Add Flags checking in Hello TLV

[zmw12306]

According to RFC 8966: https://www.rfc-editor.org/rfc/rfc8966#name-hello

X: all other bits MUST be sent as 0 and silently ignored on reception

This means the Flags field could either be BABEL_UNICAST_HELLO 0x8000 or BABEL_MULTICAST_HELLO 0x0000, otherwise it is an invalid packet.

[donaldsharp]

can you put your analysis about what is going on in the actual commit itself?

[zmw12306]

can you put your analysis about what is going on in the actual commit itself?

This commit checks whether it is a valid MULTICAST hello, if not, the code logs a debug message and stops processing the packet. Do you want me to add this to the commit message?

[riw777]

can you put your analysis about what is going on in the actual commit itself?

This commit checks whether it is a valid MULTICAST hello, if not, the code logs a debug message and stops processing the packet. Do you want me to add this to the commit message?

Yes, that would be great.

[riw777]

waiting on commit message and clearing ci

[riw777]

failure looks related --

=========================== short test summary info ============================
FAILED babel_topo1/test_babel_topo1.py::test_zebra_ipv4_routingTable - Assert...
============= 1 failed, 1 passed, 1 skipped, 2 warnings in 45.37s ==============
Some rerun tests still failed.```

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.