docs(core.config.auth.databases.ldap): fix LDAP filter config variable

[spaceone]

Hello,
https://doc.dovecot.org/2.4.4/core/config/auth/databases/ldap.html#ldap-userdb

documents two variants to specify the LDAP filter:

userdb ldap {
  filter = (&(objectClass=posixAccount)(uid=%{user}))
  fields {
    home = %{ldap:homeDirectory}
    uid = %{ldap:uidNumber}
    gid = %{ldap:gidNumber}
  }
}

userdb ldap-user {
  driver = ldap
  result_success = continue-ok
  ldap_filter = (&(objectClass=posixAccount)(uid=%{user}))
  fields {
    class = %{ldap:userClass}
  }
}

either as filter or as ldap_filter.
I didn't find the source code, where this is parsed.
But I assume ldap_filter in a userdb/passwd block is wrong. Only the global options are prefixed with ldap_.

[cmouse]

The reason is that the real setting name is passdb_ldap_filter. There is bit of magic parsing here.

passdb ldap {
   filter
}

gets expanded into this by virtue of having passdb and ldap in the block name.

if you have

passdb users {
  driver = ldap
  ldap_filter
}

you need the ldap_ prefix, or you could use passdb_ldap_filter.

[spaceone]

alright, this is now more logical to me.
Then I close this MR.