openvpn: fix compile error with musl

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 41425

package/network/services/openvpn/patches/110-musl_compat.patch

@@ -0,0 +1,13 @@
+--- a/src/openvpn/syshead.h
++++ b/src/openvpn/syshead.h
+@@ -214,10 +214,6 @@
+ 
+ #ifdef TARGET_LINUX
+ 
+-#if defined(HAVE_NETINET_IF_ETHER_H)
+-#include <netinet/if_ether.h>
+-#endif
+-
+ #ifdef HAVE_LINUX_IF_TUN_H
+ #include <linux/if_tun.h>
+ #endif