etherwake: fix musl compatibility

Always include net/ethernet.h instead linux specific headers,
fixes compilation with musl libc.

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

net/etherwake/patches/120-musl-compat.patch

@@ -0,0 +1,17 @@
+--- a/ether-wake.c
++++ b/ether-wake.c
+@@ -82,14 +82,8 @@ static char usage_msg[] =
+ #include <linux/if.h>
+ 
+ #include <features.h>
+-#if __GLIBC__ >= 2 && __GLIBC_MINOR >= 1
+ #include <netpacket/packet.h>
+ #include <net/ethernet.h>
+-#else
+-#include <asm/types.h>
+-#include <linux/if_packet.h>
+-#include <linux/if_ether.h>
+-#endif
+ #include <netdb.h>
+ #include <netinet/ether.h>
+