LU-15635 ldiskfs: Interface change fix server v5.10

LU-15635 ldiskfs: Interface change fix server v5.10

Linux v5.9-rc7-8-g15ed2851b0f4
    ext4: remove unused argument from ext4_(inc|dec)_count

Test for ext4_inc_count with 2 arguments and provide a compat
wrapper for ldiskfs_inc|dec_count that discards handle has
needed.

Lustre-change: https://review.whamcloud.com/46775
Lustre-commit: 68d96d2f650a6d9ae04e48eac9c66b2cd4be0a23

HPE-bug-id: LUS-10808
Fixes: c93a3e5b15 ("LU-14195 ldiskfs: update patches for Linux 5.10")
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I48fb52e67ad334e2fc0c045e96fc5dffd3243842
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/47731
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>