systemd: Enable ProtectHome and ProtectSystem options

These options protect from unintended access to the filesystem see
SYSTEMD.EXEC(5) for mode detail.
diff --git a/src/bluetooth.service.in b/src/bluetooth.service.in
index 83e4732..f799f65 100644
--- a/src/bluetooth.service.in
+++ b/src/bluetooth.service.in
@@ -12,6 +12,8 @@
 #Restart=on-failure
 CapabilityBoundingSet=CAP_NET_ADMIN CAP_NET_BIND_SERVICE
 LimitNPROC=1
+ProtectHome=true
+ProtectSystem=full
 
 [Install]
 WantedBy=bluetooth.target