fff-sysupgrade: move /etc/sysupgrade.sh to /sbin/fff-upgrade.sh

The old name "sysupgrade.sh" is easy to be confused with OpenWrt's
/sbin/sysupgrade. Rename our script to clearly indicate its
purpose.

While at it, move from /etc to /sbin, as the former is an odd location
for an executable script.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Robert Langhammer <rlanghammer@web.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>

src/packages/fff/fff-sysupgrade/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=fff-sysupgrade
-PKG_RELEASE:=10
+PKG_RELEASE:=11
 
 PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)