LU-13274 uapi: fix build on older kernels

LU-13274 uapi: fix build on older kernels

The recent changes to lustre_user.h broke building on older kernels,
because it resulted in the user tools including both <linux/quota.h>
and <sys/quota.h>, which results in conflicts for the declaration of
the quotactl() function.

Also, restore the compat declaration of __ALIGN_KERNEL(), though it
only in lustre_user.h, since it is included in other headers anyway.

Test-Parameters: trivial
Fixes: 0417dce9fc75 ("LU-13274 uapi: make lustre UAPI headers C99 compliant")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I9b31cabaf2732eb5872e88686e6af7d12e7d3564
Reviewed-on: https://review.whamcloud.com/38520
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>