Follow the lead set by Jeff: no need to run AC_CONFIG_HEADERS on orte_config.h. However, unlike the MPI layer, we don't run that macro on another file in orte/include, so ensure we add that -I path back!
pml/ob1: fix heterogeneous support when using the send_inline optimization

We will track #4568 from the 1.8 CMR.

Closes #4568

cmr=v1.8.2:reviewer=jsquyres