add rpath on mca_mtl_mxm.so to point to /path/to/mxm/lib/libmxm.so which was detected at configure time
This *should* fix following situation:

1 mxm.rpm puts /etc/ld.so.conf.d/mxm.conf file during rpm install with libpath to /opt/mellanox/mxm/lib
2 some1 can extract mxm.rpm into $HOME/mxm and compile OMPI with new mxm location
3 during runtime, OMPI from prev step will pick MXM from step (1) instead of from step (2)

cmr=v1.7.4:reviewer=ompi-rm1.7
Fix compiler errors on Solaris, NetBSD, and OpenBSD:

 * Per
   http://www.open-mpi.org/community/lists/devel/2013/12/13504.php, 
   protect usage of struct ifreq->ifr_hwaddr
 * Per
   http://www.open-mpi.org/community/lists/devel/2013/12/13503.php,
   avoid #define conflict with the token "if_mtu"
 * Also fix some whitespace and string naming issues in opal/util/if.c

Tested by Paul Hargrove.

Refs #4010
As reported by Paul Hargrove
(http://www.open-mpi.org/community/lists/devel/2013/12/13521.php),
OpenBSD-5 #define's MIN and MAX, so we need to #undef them.

cmr=v1.7.4:reviewer=rhc:subject=undef MIN and MAX for OpenBSD-5