[packages] tinc: The initscript for tinc writes a temporary config into /tmp/tinc.

[packages] tinc: The initscript for tinc writes a temporary config into /tmp/tinc.
In the prepare_net function it appends flags and params from the uci config to
the temporary tinc.conf for each net. These values are appended to the
config file on each /etc/init.d/tinc restart and the file grows. By
removing all old temporary config this problem is solved. Then we should
also remove the temporary config for a net which is stopped to free up
some bytes in memory.
Contribution from Manuel Munz <freifunk@somakoma.de>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@35053 3c298f89-4303-0410-b956-a3cf2f4a3e73