Revert "vnstat: update to v1.16"

This reverts commit 79b6e9dc61.

Undo the recent vnstat update due to upstream bugs preventing database
restoration.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

net/vnstat/patches/001-conf.patch

@@ -0,0 +1,19 @@
+--- a/cfg/vnstat.conf
++++ b/cfg/vnstat.conf
+@@ -78,13 +78,13 @@ DaemonUser ""
+ DaemonGroup ""
+ 
+ # how often (in seconds) interface data is updated
+-UpdateInterval 30
++UpdateInterval 60
+ 
+ # how often (in seconds) interface status changes are checked
+-PollInterval 5
++PollInterval 30
+ 
+ # how often (in minutes) data is saved to file
+-SaveInterval 5
++SaveInterval 30
+ 
+ # how often (in minutes) data is saved when all interface are offline
+ OfflineSaveInterval 30