qrexec: do not leak FDs to logger process

This would prevent qrexec from detecting EOF.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
(cherry picked from commit 7b582e0339)

qrexec/qubes-rpc-multiplexer

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 mkfifo /tmp/qrexec-rpc-stderr.$$
-logger -t "$1-$2" -f /tmp/qrexec-rpc-stderr.$$ &
+logger -t "$1-$2" -f /tmp/qrexec-rpc-stderr.$$ >/dev/null 2>&1 </dev/null &
 exec 2>/tmp/qrexec-rpc-stderr.$$
 rm -f /tmp/qrexec-rpc-stderr.$$