Protect the container_of #define.
    
MOFED apparently has a /usr/include/infiniband/verbs.h that also
defines a (slightly different but fully compatible) container_of
macro.  So put proper #ifndef protection around our definition of
container_of.

Thanks to Rolf vandeVaart for pointing out the issue.

Reviewed by Dave Goodell.

cmr=v1.7.4:reviewer=ompi-rm1.7