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>

fs/smb/client/smb2ops.c

@@ -2683,6 +2683,7 @@ smb2_queryfs(const unsigned int xid, struct cifs_tcon *tcon,
 		smb2_copy_fs_info_to_kstatfs(info, buf);
 
 qfs_exit:
+	trace_smb3_qfs_done(xid, tcon->tid, tcon->ses->Suid, tcon->tree_name, rc);
 	free_rsp_buf(buftype, rsp_iov.iov_base);
 	return rc;
 }

fs/smb/client/trace.h

@@ -691,7 +691,7 @@ DEFINE_EVENT(smb3_tcon_class, smb3_##name,    \
 	TP_ARGS(xid, tid, sesid, unc_name, rc))
 
 DEFINE_SMB3_TCON_EVENT(tcon);
-
+DEFINE_SMB3_TCON_EVENT(qfs_done);
 
 /*
  * For smb2/smb3 open (including create and mkdir) calls