ipn/ipnlocal: add missing place where we set the SSH atomic

This fixes the "tailscale up --authkey=... --ssh" path (or any "up"
path that used Start instead of EditPrefs) which wasn't setting the
bit.

Updates #3802

Change-Id: Ifca532ec58296fedcedb5582312dfee884367ed7
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -955,6 +955,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 				b.logf("failed to save UpdatePrefs state: %v", err)
 			}
 		}
+		b.setAtomicValuesFromPrefs(b.prefs)
 	}
 
 	wantRunning := b.prefs.WantRunning