Set size of IMMED data in RMA packets to 8 bytes.

Originally the size of IMMED data in RMA packets is 16 bytes
which makes the size of CH3 packet be 56 bytes. Here we reduce
the size of IMMED data in RMA packets to 8 bytes, so that the
size of CH3 packet is reduced to 48 bytes, the same with
mpich-3.1.4 (the old RMA infrastructure).
Signed-off-by: Min Si <msi@il.is.s.u-tokyo.ac.jp>
Signed-off-by: Antonio J. Pena <apenya@mcs.anl.gov>

src/mpid/ch3/include/mpidpkt.h

@@ -23,7 +23,7 @@
 #define MPIDI_EAGER_SHORT_SIZE 16
 
 /* This is the number of ints that can be carried within an RMA packet */
-#define MPIDI_RMA_IMMED_BYTES 16
+#define MPIDI_RMA_IMMED_BYTES 8
 
 /* Union over all types (integer, logical, and multi-language types) that are
    allowed in a CAS operation.  This is used to allocate enough space in the