Babel: Add a test capture file

Babel: Add a test capture file

This capture file triggered a buffer over-read with the 4.9.2 release
fixed in the 4.9.3 release.

With the new GET_ macros, the problem no longer exists.
Thus no fix needed.

The pcap file was updated to pass the sanity checks and to avoid
pcap_loop() error messages.

Moreover:
Fix an existing length check.

Update the output of the test accordingly.

Partial update from 12f66f69f7bf1ec1266ddbee90a7616cbf33696b
in 4.9 branch.