libpfring: Fix compilation when missing lex

Buildbots are missing lex, which is normally a symlink to flex. This
solution is used elsewhere in the package but missing here.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/libpfring/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libpfring
 PKG_VERSION:=7.2.0
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_MAINTAINER:=Banglang Huang <banglang.huang@foxmail.com>
 
 PKG_LICENSE:=LGPL-2.1

libs/libpfring/patches/010-fix-buildbots.patch

@@ -0,0 +1,10 @@
+diff --git a/userland/nbpf/Makefile.in b/userland/nbpf/Makefile.in
+index b0d8181..8221e41 100644
+--- a/userland/nbpf/Makefile.in
++++ b/userland/nbpf/Makefile.in
+@@ -1,4 +1,4 @@
+-LEX = lex
++LEX = flex
+ YACC = bison
+ INCLUDE = -I../lib -I../../kernel
+ LIBS=`../lib/pfring_config --libs` -lpthread #@NDPI_LIB@