NA BMI: bug fix to bmi tags for internal RMA emulation (#265)
NA BMI: bug fix to bmi tags for internal RMA emulation (#265)

- differentiate tags used for different RMA control steps by reserving 8
  bits of tag space
- this prevents (for example) the payload msg of one RMA operation from
  colliding with a control msg of a different RMA, when the tags are
  chosen by two different hosts independently.
mercury-hpc/mercury,mercury-hpc/mercury,mercury-hpc/mercury,mercury-hpc/mercury