Re-arm TCP_QUICKACK once per read batch in bus connection

TCP_QUICKACK is a one-shot option that the kernel clears after each ACK.
`ReadSocket` re-armed it on every call, but `OnSocketRead` invokes `ReadSocket`
in a loop, draining the socket in `ReadBufferSize`/`MaxBatchReadSize` chunks — so
a single readable event issued one `setsockopt` syscall per chunk even though
all those reads produce at most one ACK. Move the re-arm to once per
`OnSocketRead` batch, gated on having read something; behavior is unchanged (the
ACK for the just-received data is still armed after the socket is drained).

Found while profiling `BusXferFS` threads on an RPC proxy: the per-chunk
`setsockopt` showed up in the read path. Minor on its own (~0.3% there), but a
clean cleanup.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
commit_hash:8a26370d548994ae3ab008f5d901df2e51bfff6d

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