Over time all taildrop functionality will be contained in the
taildrop package. This will include end to end unit tests. This is
simply the first smallest piece to move over.
There is no functionality change in this commit.
Updates tailscale/corp#14772
Signed-off-by: Rhea Ghosh <rhea@tailscale.com>
Co-authored-by: Joseph Tsai <joetsai@tailscale.com>
