treewide: Change .*GPL.*+ licenses to SPDX compatible identifier

The CONTRIBUTING.md requests an (or multiple) SPDX identifier for GPL
licenses. But a lot of packages did use a different, non-SPDX style with a
"+" at the end instead of "-or-later".

Signed-off-by: Sven Eckelmann <sven@narfation.org>

libs/libesmtp/Makefile

@@ -9,10 +9,10 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libesmtp
 PKG_VERSION:=1.0.6
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_MAINTAINER:=Othmar Truniger <github@truniger.ch>
-PKG_LICENSE:=LGPL-2.0+
+PKG_LICENSE:=LGPL-2.0-or-later
 PKG_LICENSE_FILES:=COPYING
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2