integck: fix build error (MS_DIRSYNC, MS_RELATIME)

integck: fix build error (MS_DIRSYNC, MS_RELATIME)

Need to include <linux/fs.h>, at least for my build system. Otherwise,
you can't build the 'tests'.

integck.c: In function ‘parse_mount_options’:
integck.c:2862: error: ‘MS_DIRSYNC’ undeclared (first use in this
function)
integck.c:2862: error: (Each undeclared identifier is reported only once
integck.c:2862: error: for each function it appears in.)
integck.c:2872: error: ‘MS_RELATIME’ undeclared (first use in this
function)

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>