meta-google: nftables-systemd: Flush at start

We don't want errors in loading previous rules to affect the state of the
ruleset during restart.

Change-Id: Ic122e971670d56022029f1155c1accdf129672d0
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meta-google/recipes-google/nftables/files/nftables.service b/meta-google/recipes-google/nftables/files/nftables.service
index 79f0bb5..770a3d3 100644
--- a/meta-google/recipes-google/nftables/files/nftables.service
+++ b/meta-google/recipes-google/nftables/files/nftables.service
@@ -5,7 +5,7 @@
 Type=oneshot
 RemainAfterExit=yes
 ExecStart=/usr/libexec/nft-configure.sh
-ExecStop=/bin/bash -c 'nft flush ruleset'
+ExecStop=/usr/sbin/nft flush ruleset
 
 [Install]
 WantedBy=multi-user.target