Switch to killing cshark with -TERM instead of -INT

Killing the cshark program by sending the -INT signal was no longer
working and cshark would keep running indefinitely. Changing this to
kill cshark with the -TERM signal did kill cshark and still cleaned up
all of the temporary files in /tmp, pid file, capture file, and cshark
stdout file. The LuCI interface also printed out the correct information
and added the uploaded capture to the list of uploaded captures.

openwrt/luci/luasrc/controller/cshark.lua

@@ -64,7 +64,7 @@ function cshark_iface_dump_stop()
 	local pid = f:read("*all")
 	io.close(f)
 
-	local res = os.execute("kill -INT " .. pid)
+	local res = os.execute("kill -TERM " .. pid)
 	luci.http.write(tostring(res))
 end