LU-18231 obd: change obd_attach into ODBF_ATTACH

LU-18231 obd: change obd_attach into ODBF_ATTACH

Change the use of the odb_attach bitfield into a bit in
the ofd_flags bitmap and use atomic bit set/clear/test
operations on it.
No logical changes to the code and no changes to locking.

Test-Parameters: trivial
Signed-off-by: Ronnie Sahlberg <rsahlberg@whamcloud.com>
Change-Id: I2f360f6074e2078fa20b770b5dc2abc173766c9f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56413
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>