[PATCH][SMB3] Add ftrace support

[Steve French]

 I plan to add various tracepoints to cifs.ko, but wanted to verify
that the initial patch looks ok (which only adds logging for one
event, write errors), before I start adding various other tracepoints.

Also I need to know ... is the size of log entries a problem? I have
to weight logging just the tree id (and relying on an ioctl or
proc/fs/cifs call to resolve the numeric tree id to a more readable
UNC name ie \\server\share for the mount)?

Generally I want to log these four things
tree id
session id
file id (for everything but open/tree connect/negprot/session setup
where it is not applicable) and/or file name (is logging file name
going to make log entries too big?)
xid (so we can correlate events from one syscall)