LU-17535 gss: fix lsvcgssd crash in krb lib

LU-17535 gss: fix lsvcgssd crash in krb lib

This patch fixes some logic around the need to call
gss_delete_sec_context() or not vs kerberos implementations.

snd->ctx address instead of value should be passed to
serialize_context_for_kernel()/serialize_krb5_ctx() to
allow each implementation to clear it with GSS_C_NO_CONTEXT
if it has been destroyed internally, and cases where not
can also be handled in handle_krb() now.

Test-Parameters: trivial
Test-Parameters: kerberos=true testlist=sanity-krb5
Test-Parameters: testgroup=review-dne-selinux-ssk-part-2
Signed-off-by: Bruno Faccini <bfaccini@nvidia.com>
Change-Id: I752712168a2c0f0a5a7a496b851d4cddbb7e4236
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54023
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Aurelien Degremont <adegremont@nvidia.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>