LU-17907 enc: enc flag should not remove other flags

LU-17907 enc: enc flag should not remove other flags

When updating inode flags, the lli_flags must be taken into account
so that they do not get lost. So provide helper functions for callers
of ll_update_inode_flags(), as an overlay to ll_inode_to_ext_flags().
And on server side, the mdd layer must fetch the existing flags when
setting LUSTRE_ENCRYPT_FL attr flag.

Fixes: 40d91eafe2 ("LU-12275 sec: atomicity of encryption context getting/setting")
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I150f2d87cef112beab81d1d2030133671d4b7361
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55317
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>