smb3: add trace point for queryfs (statfs)

In debugging a recent performance problem with statfs, it would have
been helpful to be able to trace the smb3 query fs info request
more narrowly.  Add a trace point "smb3_qfs_done"

Which displays:

 stat-68950   [008] .....  1472.360598: smb3_qfs_done: xid=14 sid=0xaa9765e4 tid=0x95a76f54 unc_name=\\localhost\test rc=0

Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>