security/sssd2: Add patch to enumerate UIDs

The legacy security/sssd port has a patch which lets one set
krb5_store_password_if_offline=True in a IPA provider configuration
block. The patch fixes some code which uses /proc to enumerate the UIDs
of logged-in users. Without the patch, if one has this configuration
variable set, sssd dies with an obscure error. This caused some pain
when a user was updating from sssd to sssd2.

Sponsored by: Serenity Cybersecurity, LLC

PR: 279255
Reported by: markj@freebsd.org, arrowd@freebsd.org
Obtained from: arrowd@freebsd.org