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>

net/banip/Makefile

@@ -7,8 +7,8 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=banip
 PKG_VERSION:=0.2.0
-PKG_RELEASE:=1
-PKG_LICENSE:=GPL-3.0+
+PKG_RELEASE:=2
+PKG_LICENSE:=GPL-3.0-or-later
 PKG_MAINTAINER:=Dirk Brenken <dev@brenken.org>
 
 include $(INCLUDE_DIR)/package.mk