Add libibverbs-dev to Dockerfile

[Aphoh]

Motivation

Currently when running sglang in a multi-node configuration with infiniband and NCCL_DEBUG=INFO, the logs will contain

...
NCCL INFO Failed to open libibverbs.so[.1]
...
NCCL INFO NET/Socket : Using [0]ib0.<ip>
...

This means all-reduces will be performed over TCP instead of gpu RDMA. In the VLLM containers, they fix this by installing libibverbs-dev here

Doing so in sglang's docker container fixes this issue and greatly speeds up multi-node deployments.

Modifications

Add libibverbs-dev to the installed dependencies in the Dockerfile.

Checklist

• [ x] Format your code according to the Contributor Guide.
• [x ] Add unit tests as outlined in the Contributor Guide.
• [x ] Update documentation as needed, including docstrings or example tutorials.