LU-17317 sec: add srpc_serverctx proc file

LU-17317 sec: add srpc_serverctx proc file

GSS srpc contexts for client connections can already be dumped via
proc file <mdc,osc>.*.srpc_contexts.
This patch adds a new proc file to dump server side GSS srpc contexts,
e.g.:
mgs.MGS.gss.srpc_serverctx
mdt.testfs-MDT0000.gss.srpc_serverctx
obdfilter.testfs-OST0000.gss.srpc_serverctx

The GSS context information is dumped as YAML, with one line per
context, like this:
- 0000000013221bdf: { peer_nid: 192.168.56.206@tcp, uid: 0, ctxref: 1,
expire: 1707934985, delta: 3401, flags: [uptodate, cached], seq: 0,
win: 2048, key: 00000000, keyref: 0,
hdl: "0x5ae1a771fd57043:0x65a64972fda4e200",
mech: "krb5 (aes256-cts-hmac-sha1-96)" }

Because of this new syntax, sanity-sec test_28 needs to be fixed.

Test-Parameters: trivial
Test-Parameters: kerberos=true testlist=sanity-krb5
Test-Parameters: testgroup=review-dne-selinux-ssk-part-2
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I37da9ffe6dd5884006b36271185a4d7155ead65b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53376
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Aurelien Degremont <adegremont@nvidia.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>