Minor fixes:
* The branch for listing or hashing partial files was inverted.
* The host for peerapi call needs to be real (rather than bogus).
* Handle remote peers that don't support resuming.
* Make resume failures non-fatal (since we can still continue).
This was tested locally, end-to-end system test is future work.
Updates tailscale/corp#14772
Signed-off-by: Joe Tsai <joetsai@digital-static.net>
Co-authored-by: Rhea Ghosh <rhea@tailscale.com>
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