This commit is based on ff0978ab, and extends #18497 to connect network map
caching to the LocalBackend. As implemented, only "whole" netmap values are
stored, and we do not yet handle incremental updates. As-written, the feature must
be explicitly enabled via the TS_USE_CACHED_NETMAP envknob, and must be
considered experimental.
Updates #12639
Co-Authored-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I48a1e92facfbf7fb3a8e67cff7f2c9ab4ed62c83
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
f4aea70f7a