connection: rename kdbus_check_send_perm() to kdbus_conn_check_access()

Keep the function namespace clean.
connection: clean up conditional code path

For broadcasts, we return anway, so there's no point in an 'else' branch.
connection: don't append to uninitialized metadata

kmsg->meta is only valid if conn_src != NULL.
Fix annoying compile warning due to missing cast
test: correctly set the 'ret' variable

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
domain: add kdbus_domain_user_assign_id() to assign IDs to domain users

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
domain: add __kdbus_domain_user_account() to account domain users

Add __kdbus_domain_user_account() to account and link users into a
domain.

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
domain: add kdbus_domain_user_account()

Add kdbus_domain_user_account() to account and link users into a
domain.

This function will take the domain lock, and it will be used as a
replacement for kdbus_domain_user_find_or_new().

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>