KRB5: Fix access_provider=krb5
    
    The domain type (posix or not) was being sent to the krb5_child always,
    but the buffer only had enough space in case of authentication, not
    authorization. Bug was introduced in the commit
      861ab44e8148208425b67c4711bc8fade10fd3ed
    
    This patch makes the buffer one uint32_t unit larger.
    
    To reproduce, just set up sssd.conf with:
        access_provider = krb5
    
    Without the patch, you would see messages like:
        ==14111== Invalid write of size 2
        ==14111==    at 0x4C3041B: memcpy@@GLIBC_2.14 (vg_replace_strmem.c:1018)
        ==14111==    by 0xE0EE275: safealign_memcpy (util_safealign.h:51)
        ==14111==    by 0xE0EECB3: create_send_buffer (krb5_child_handler.c:239)
        ==14111==    by 0xE0EFDDE: handle_child_send (krb5_child_handler.c:529)
        ==14111==    by 0xE0EDEDD: krb5_access_send (krb5_access.c:149)
        ==14111==    by 0xE0ED32F: krb5_pam_handler_send (krb5_auth.c:1250)
        ==14111==    by 0x418868: file_dp_request (dp_request.c:254)
        ==14111==    by 0x418976: dp_req_send (dp_request.c:300)
        ==14111==    by 0x41C25F: dp_pam_handler (dp_target_auth.c:219)
        ==14111==    by 0x52B3456: sbus_request_invoke_or_finish (sssd_dbus_request.c:71)
        ==14111==    by 0x52B0F37: sbus_message_handler_got_caller_id (sssd_dbus_interface.c:1048)
        ==14111==    by 0x923C923: tevent_common_loop_immediate (tevent_immediate.c:135)
        ==14111==  Address 0x126ab506 is 150 bytes inside a block of size 151 alloc'd
        ==14111==    at 0x4C2BBAD: malloc (vg_replace_malloc.c:299)
        ==14111==    by 0x944D7F4: __talloc_with_prefix (talloc.c:698)
        ==14111==    by 0x944D7F4: __talloc (talloc.c:739)
        ==14111==    by 0x944D7F4: _talloc_named_const (talloc.c:896)
        ==14111==    by 0x944D7F4: talloc_named_const (talloc.c:1675)
        ==14111==    by 0xE0EE7B6: create_send_buffer (krb5_child_handler.c:185)
        ==14111==    by 0xE0EFDDE: handle_child_send (krb5_child_handler.c:529)
        ==14111==    by 0xE0EDEDD: krb5_access_send (krb5_access.c:149)
        ==14111==    by 0xE0ED32F: krb5_pam_handler_send (krb5_auth.c:1250)
        ==14111==    by 0x418868: file_dp_request (dp_request.c:254)
        ==14111==    by 0x418976: dp_req_send (dp_request.c:300)
        ==14111==    by 0x41C25F: dp_pam_handler (dp_target_auth.c:219)
        ==14111==    by 0x52B3456: sbus_request_invoke_or_finish (sssd_dbus_request.c:71)
        ==14111==    by 0x52B0F37: sbus_message_handler_got_caller_id (sssd_dbus_interface.c:1048)
        ==14111==    by 0x923C923: tevent_common_loop_immediate (tevent_immediate.c:135)
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3418
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>