LU-14651 uapi: rename CONFIG_T_* to MGS_CFG_T_*

LU-14651 uapi: rename CONFIG_T_* to MGS_CFG_T_*

The Linux kernel uses CONFIG_* as a way to determine if a feature
is available. Using CONFIG_* in an UAPI is considered an error
and in the most recent kernels will break a build. While we don't
have any CONFIG_* in our UAPI headers we do have CONFIG_T_*
which is used for config logs. This naming confuses the Linux
kernel build system so just rename these variables to MGS_CFG_T_*
instead.

Lustre-change: https://review.whamcloud.com/43494
Lustre-commit: 4d5a2eba617780eadf172cb5c1fc28d5ab023a97

Test-Parameters: trivial
Change-Id: I574510c2da90e9ae608c9e2374d75220b7abb19d
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46245
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>