missing include in infiniband

use of IS_ERR/PTR_ERR in infiniband/core/agent.c, without
a portable chain of includes pulling err.h (breaks on a bunch of platforms).

----

diff -urN RC14-base/drivers/infiniband/core/agent.h current/drivers/infiniband/core/agent.h
@@ -39,6 +39,7 @@
 #ifndef __AGENT_H_
 #define __AGENT_H_
 
+#include <linux/err.h>
 #include <rdma/ib_mad.h>
 
 extern int ib_agent_port_open(struct ib_device *device, int port_num);

Looks good to me:

I guess I still need to a few more cross-compilers to me collection -- none of i386, x86_64, ppc64, ia64, sparc64 or ppc caught this :(.

- R.