macOS Sandbox: Add (begin) to sysctl rules for tcsm.

The sysctl rules are currently incorrectly enclosed in an if/else
statement, when it should be a single if clause.

Bug: 963490
Change-Id: I9b6cf6676dd3eb8597b7d4cb4f78518112552a54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1620911
Auto-Submit: Greg Kerr <kerrnel@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661466}
2 files changed