LU-17015 gss: support large kerberos token on client side

LU-17015 gss: support large kerberos token on client side

If the current Kerberos setup is using large token, like
when MS-PAC feature is enabled, client can crash.

Instead of asserting, return E2BIG to avoid the crash
and increase the default buffer size to 4kB instead of 1kB.
This will only increase the SEC_CTX_INIT RPC size accordingly
as the buffer is shrunk before being sent over the wire.

Up to 2kB security token will be properly handled by Lustre.
But, above that size, a different issue will happen on
server side that will require an other patch.

Test-Parameters: kerberos=true testlist=sanity-krb5
Signed-off-by: Aurelien Degremont <adegremont@nvidia.com>
Change-Id: I9ce30ee7f8c95bfe41525c49986ffac45ffac97c