tor: preserve tor keys over sysupgrade

Mark the directories containing the keys for hidden services as
conffiles to preserve them over sysupgrade.

Fixes: #2247

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

net/tor/Makefile

@@ -61,6 +61,8 @@ endef
 
 define Package/tor/conffiles
 /etc/tor/torrc
+/var/lib/tor/fingerprint
+/var/lib/tor/keys/*
 endef
 
 CONFIGURE_ARGS += \