LU-1904 idl: add checks for OBD_CONNECT flags

LU-1904 idl: add checks for OBD_CONNECT flags

Make it harder to accidentally declare OBD_CONNECT flags without
properly defining their names.  Otherwise, this can cause serious
compatibility problems if two features are using the same flag.

Add the definition lines into spelling.txt so there is *always*
a warning generated, since this always needs proper attention.

Make it clear whom to contact when reserving a new feature flag.

Lustre-change: https://review.whamcloud.com/48053
Lustre-commit: d851381ea6947244842ae6f138cd0bfd399b7ef4

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I9a5e2c97c40c39ea57d20979d4b130854edc785a
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51408
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>