TT#182450 systemd hardening: allow R/W access to /var/spool/rtpengine

By default we use /var/spool/rtpengine as recording directory,
so ensure we have R/W access to it.

Change-Id: I4abf4df218b1ba0dc70ed8974c0661d16e0b6ea7
(cherry picked from commit 26bf2b05a5)

debian/ngcp-rtpengine-daemon.service

@@ -43,6 +43,9 @@ ProtectKernelTunables=true
 # Service has strict read-only access to the OS file hierarchy
 ProtectSystem=strict
 
+# Allow write access
+ReadWritePaths=/var/spool/rtpengine
+
 # Access to the kernel log ring buffer will be denied
 ProtectKernelLogs=true