configure: also check for byteswap.h

include/f2fs_fs.h checks the HAVE_BYTESWAP_H conditional, but it is
never checked for in configure.

Add that header to the list of headers checked for.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/configure.ac b/configure.ac
index d66cb73..7cfd9b4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -57,7 +57,7 @@
 
 # Checks for header files.
 AC_CHECK_HEADERS([linux/fs.h fcntl.h mntent.h stdlib.h string.h \
-		sys/ioctl.h sys/mount.h unistd.h linux/falloc.h])
+		sys/ioctl.h sys/mount.h unistd.h linux/falloc.h byteswap.h])
 
 # Checks for typedefs, structures, and compiler characteristics.
 AC_C_INLINE