base-files: rc.common: fix enable() return code and logic

In current state, if there is START but no STOP, enbale()
will return 1 (failure), which is wrong.
Moreover there is no need to check for START/STOP twice.
Instead, add err variable to save success state and
and return it's value.
Also eliminate the need to disable() by using 'ln -sf',
which will first delete the old symlink if one exists.

Changes from v1:
- fixed description

Signed-off-by: Roman Yeryomin <roman@advem.lv>

package/base-files/files/etc/rc.common

@@ -41,14 +41,15 @@ disable() {
 }
 
 enable() {
+	err=1
 	name="$(basename "${initscript}")"
-	disable
-	[ -n "$START" -o -n "$STOP" ] || {
-		echo "/etc/init.d/$name does not have a START or STOP value"
-		return 1
-	}
-	[ "$START" ] && ln -s "../init.d/$name" "$IPKG_INSTROOT/etc/rc.d/S${START}${name##S[0-9][0-9]}"
-	[ "$STOP"  ] && ln -s "../init.d/$name" "$IPKG_INSTROOT/etc/rc.d/K${STOP}${name##K[0-9][0-9]}"
+	[ "$START" ] && \
+		ln -sf "../init.d/$name" "$IPKG_INSTROOT/etc/rc.d/S${START}${name##S[0-9][0-9]}" && \
+		err=0
+	[ "$STOP" ] && \
+		ln -sf "../init.d/$name" "$IPKG_INSTROOT/etc/rc.d/K${STOP}${name##K[0-9][0-9]}" && \
+		err=0
+	return $err
 }
 
 enabled() {