s3:smbd: fix SMB2 aio cancelling

As we currently don't attempt to cancel the internal aio request, we
must ignore the SMB2 cancel request and continue to process the SMB2
request, cf MS-SM2 3.3.5.16:

  If the target request is not successfully canceled, processing of the
  target request MUST continue and no response is sent to the cancel
  request.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13667

Signed-off-by: Ralph Boehme <slow@samba.org>
22 jobs for slow-autobuild in 90 minutes and 31 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build_ctdb #113617454
docker shared

00:37:24

passed build_others #113617456
docker shared

00:14:12

failed build_samba #113617459
docker private

01:26:46

passed build_samba_ad_dc #113617464
docker private

01:30:28

passed build_samba_ad_dc_2 #113617448
docker shared

00:41:04

passed build_samba_ad_dc_2_py3 #113617449
docker shared

00:28:08

passed build_samba_ad_dc_py3 #113617465
docker private

00:21:34

passed build_samba_buildpy3_only #113617457
docker shared

00:26:19

passed build_samba_ctdb #113617455
docker shared

00:20:37

passed build_samba_fileserver #113617463
docker private

00:20:38

passed build_samba_libs #113617450
docker shared

00:34:21

passed build_samba_libs_py3 #113617451
docker shared

00:35:31

passed build_samba_none_env #113617443
docker shared

00:46:56

passed build_samba_nopython #113617444
docker shared

00:28:39

passed build_samba_nt4 #113617461
docker private

00:40:02

passed build_samba_nt4_py3 #113617462
docker private

00:12:46

passed build_samba_o3 #113617447
docker shared

00:32:18

passed build_samba_purepy3-none_env #113617458
docker shared

01:10:47

passed build_samba_py3 #113617460
docker private

01:26:06

passed build_samba_static #113617452
docker shared

00:45:23

passed build_samba_systemkrb5 #113617445
docker shared

00:15:50

passed build_samba_xc #113617446
docker shared

00:06:40

 
Name Stage Failure
failed
build_samba Build
/dev/xvda1        317594  3683    313896   2% /builds/samba-team/devel


### df -m /tmp/samba-testbase/b14
Filesystem 1M-blocks Used Available Use% Mounted on
/dev/mapper/docker-202:1-258580-8684e516ea66620bb14d6ecb12ee5d7b85d598b1220782007521171e03c33f11 10229 1875 8355 19% /


ERROR: Job failed: exit code 1