linux_netlink: Remove unnecessary header includes and conditionals

We always require <sys/socket.h> and do not need <linux/filter.h>.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>
diff --git a/configure.ac b/configure.ac
index ec71e62..4e35bf6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -113,14 +113,12 @@
 			AC_CHECK_LIB([udev], [udev_new], [], [AC_ERROR(["udev support requested but libudev not installed"])])
 			AC_DEFINE(USE_UDEV, 1, [Use udev for device enumeration/hotplug])
 		else
-			AC_CHECK_HEADERS([asm/types.h sys/socket.h], [], [])
-			AC_CHECK_HEADERS([linux/netlink.h linux/filter.h], [], [AC_ERROR(["Linux netlink headers not found"])], [
+			AC_CHECK_HEADERS([asm/types.h], [], [])
+			AC_CHECK_HEADERS([sys/socket.h linux/netlink.h], [], [AC_ERROR(["Linux netlink headers not found"])], [
 #ifdef HAVE_ASM_TYPES_H
 #include <asm/types.h>
 #endif
-#ifdef HAVE_SYS_SOCKET_H
 #include <sys/socket.h>
-#endif
 ])
 		fi
 		AC_SUBST(USE_UDEV)