[LNA] rename LNA net error code

Rename BLOCKED_BY_PRIVATE_NETWORK_ACCESS_CHECKS to
BLOCKED_BY_LOCAL_NETWORK_ACCESS_CHECKS; this is visible in the devtools
console to external developers; renaming it means less confusion when
they search google for BLOCKED_BY_PRIVATE_NETWORK_ACCESS_CHECKS and find
outdated advice pertaining to PNA which no longer works.

Also change the error page to not recommend reloading the subframe
navigation, as this is no longer advice that will change any outcomes.

Change-Id: I61b63c1a79565c137096960cda76eb6176280fe8
Bug: 394636065
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7008913
Reviewed-by: mmenke <mmenke@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Commit-Queue: Hubert Chao <hchao@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1526842}