net-snmp: fix musl compatibility

Fixup `iwlib.h` to not consider an musl environment to be an unsupported
platform.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

net/net-snmp/Makefile

@@ -1,5 +1,5 @@
 #
-# Copyright (C) 2006-2014 OpenWrt.org
+# Copyright (C) 2006-2015 OpenWrt.org
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=net-snmp
 PKG_VERSION:=5.4.4
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=@SF/net-snmp

net/net-snmp/patches/900-musl-compat.patch

@@ -0,0 +1,14 @@
+--- a/agent/mibgroup/iwlib.h
++++ b/agent/mibgroup/iwlib.h
+@@ -85,6 +85,11 @@
+       && LINUX_VERSION_CODE < KERNEL_VERSION(2,1,0)
+ #define LIBC5_HEADERS
+ 
++/* Musl */
++#elif !defined(__GLIBC__) && !defined(__UCLIBC__) \
++      && LINUX_VERSION_CODE >= KERNEL_VERSION(3,0,0)
++#define GENERIC_HEADERS
++
+ /* Unsupported combination */
+ #else
+ #error "Your kernel/libc combination is not supported"