IB/ipath: Make ipath_portdata work with struct pid * not pid_t

IB/ipath: Make ipath_portdata work with struct pid * not pid_t

The official reason is "with the presence of pid namespaces in the
kernel using pid_t-s inside one is no longer safe."

But the reason I fix this right now is the following:

About a month ago (when 2.6.25 was not yet released) there still was a
one last caller of a to-be-deprecated-soon function find_pid() - the
kill_proc() function, which in turn was only used by nfs callback
code.

During the last merge window, this last caller was finally eliminated
by some NFS patch(es) and I was about to finally kill this kill_proc()
and find_pid(), but found, that I was late and the kill_proc is now
called from the ipath driver since commit 58411d1c ("IB/ipath: Head of
Line blocking vs forward progress of user apps").

So here's a patch that fixes this code to use struct pid * and (!)
the kill_pid routine.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>