LU-16888 gss: fix ptlrpc_gss automatic loading

LU-16888 gss: fix ptlrpc_gss automatic loading

ptlrpc_gss kernel module is automatically loaded when a GSS security
flavor is enforced. Loading success is recorded in a static variable
in the ptlrpc module, which prevents further reloading in case
ptlrpc_gss is unloaded while keeping ptlrpc loaded.
Get rid of this static variable as it is not required in order to
avoid calling request_module("ptlrpc_gss") when not needed. Indeed,
once loaded, the static array policies[] has an entry at the
SPTLRPC_POLICY_GSS index, indicating that the ptlrpc_gss module is
loaded.

Lustre-change: https://review.whamcloud.com/51264
Lustre-commit: b80d6defb7b018250ef4fafccff7c980aed6a444

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I9bb100a202fe9c3fc455a2ffba6ee6398e19b9bf
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51374
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>