smb3: add dynamic tracepoints for shutdown ioctl

For debugging an umount failure in xfstests generic/043 generic/044 in some
configurations, we needed more information on the shutdown ioctl which
was suspected of being related to the cause, so tracepoints are added
in this patch e.g.

  "trace-cmd record -e smb3_shutdown_enter -e smb3_shutdown_done -e smb3_shutdown_err"

Sample output:
  godown-47084   [011] .....  3313.756965: smb3_shutdown_enter: flags=0x1 tid=0x733b3e75
  godown-47084   [011] .....  3313.756968: smb3_shutdown_done: flags=0x1 tid=0x733b3e75

Tested-by: Anthony Nandaa (Microsoft) <profnandaa@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>