Fix bug in MCA_PML_OB1_ADD_ACK_TO_PENDING that causes memory overruns…

[hjelmn]

… or failure

The MCA_PML_OB1_ADD_ACK_TO_PENDING method creates a mca_pml_ob1_pckt_pending_t to hold an ack to be sent later. This method builds the pending packet then puts it on the mca_pml_ob1.pckt_pending list for later transmission. It does not, however, set the required hdr_size field on the struct. This leads to issues when the packet is later sent because it could contain any value. With some btls this will lead to memory corruption (if the size is not checked against btl_max_send_size) or just allocation failure because the size is too big. In other situations it could lead to a truncated packet being send (if the size previously in hdr_size is smaller than an ack).

To fix the issue this commit gets rid of the macro entirely and replaces it with a new inline helper method that does the same thing. This helper uses the existing mca_pml_ob1_add_to_pending helper (which sets hdr_size) to reduce duplicated code.

Tested and verified this fixes a critical issue triggered on our hardware.

(cherry picked from commit 48490b9)

[bosilca]

This could have been a single line change in MCA_PML_OB1_ADD_ACK_TO_PENDING (adding _pck->hdr_size = sizeof(hdr.hdr_ack);

[hjelmn]

True, but figured it would be ideal to reduce duplicated code in case something about pending list items change (not that I expect that will ever happen).