ksmbd: add support for supplementary groups

Even though system user has a supplementary group, It gets
NT_STATUS_ACCESS_DENIED when attempting to create file or directory.
This patch add KSMBD_EVENT_LOGIN_REQUEST_EXT/RESPONSE_EXT netlink events
to get supplementary groups list. The new netlink event doesn't break
backward compatibility when using old ksmbd-tools.

Co-developed-by: Atte Heikkilä <atteh.mailbox@gmail.com>
Signed-off-by: Atte Heikkilä <atteh.mailbox@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>