Fixes docker run command to allow host receiving RA packets.

[saramonteiro]

This bring small changes for the docker run command to allow the computer (and other devices in the network) to have access to the RA packets. This a result from this issue: https://github.com/openthread/ot-br-posix/issues/1789

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[saramonteiro]

Note: Already signed the CLA.

[jwhui]

@saramonteiro , any plans to move this PR forward?