Trivial struct re-ordering to eliminate holes in the middle of the
struct (although there's still a hole at the end) and reduce the
overall size of the struct from 64 to 56 bytes. Also change mtu from
int to uint16_t; there was no need for it to be that large.
Reviewed by Dave Goodell
cmr=v1.8.2:reviewer=ompi-rm1.8
This commit was SVN r31688.