Over-estimate short and long BSR for better latency and TCP throughput

38.321 6.1.3.1 says: "The size of the RLC headers and MAC subheaders are not considered in the buffer size computation" [for BSR]. However, prior to this commit, we take the size signaled of the BSR and schedule the UE with that amount of data, making it impossible for the UE to transmit all its data at once (because it is the size signaled + headers).

In this commit, over-estimate the buffer status size. As we cannot know the exact number and size of headers, we simply use "BSR size + n", as done in function overestim_bsr_index().

We also found out that the bridge mode of the the containers had a negative impact, so convert SA B200-based tests in CI to host mode for the moment (and put a comment to use macvlan driver later).