`sturct mca_pml_ob1_comm_proc_t`, which is allocated per
connected rank in a communicator, had two paddings after
`expected_sequence` and `send_sequence` by alignments.
By changing the order of the members, the size of
`mca_pml_ob1_comm_proc_t` is reduced by 8 bytes on 64-bit
architectures.
Signed-off-by: KAWASHIMA Takahiro <t-kawashima@jp.fujitsu.com>