DAOS-19132 rdb: Fix destination ranks in log messages

[liw]

Rajesh observed log messages like these:

crt_rpc_complete_and_unlock(0x7efc3df4a620) [opc=0x7040000
  (DAOS_RDB_MODULE:) rpcid=0x3637ab4c00003653 rank:tag=102:0]
  failed, DER_OOG(-1019): 'Out of group or member list'
rdb_raft_rpc_cb() 14673705[207]: RPC 0 to rank 0 failed:
  DER_OOG(-1019): 'Out of group or member list'

Apparently, rdb_raft_rpc_cb should log 'to rank 102' instead of 'to rank 0'. The issue is that depending on when the error happens the destination rank in the request header may have yet to be initialized. This patch returns to use cr_ep.ep_rank for request senders.

Steps for the author:

• Commit message follows the guidelines.
• Appropriate Features or Test-tag pragmas were used.
• Appropriate Functional Test Stages were run.
• At least two positive code reviews including at least one code owner from each category referenced in the PR.
• Testing is complete. If necessary, forced-landing label added and a reason added in a comment.

After all prior steps are complete:

• Gatekeeper requested (daos-gatekeeper added as a reviewer).

[liw]

With this patch, sending an RDB RPC to an out-of-group rank now produces:

WARN 2026/06/10 05:51:38.011971 brd-224 DAOS[967749/0/88] rpc  src/cart/crt_context.c:519 crt_rpc_complete_and_unlock(0x7f58bc94d510) [opc=0x7050000 (DAOS_RDB_MODULE:) rpcid=0x1464ae330000006f rank:tag=3:0 orig=NOINFO] failed, DER_OOG(-1019): 'Out of group or member list'
DBUG 2026/06/10 05:51:38.011981 brd-224 DAOS[967749/0/88] rdb  src/rdb/rdb_rpc.c:359 rdb_raft_rpc_cb() 928973ff[0.1]: opc=0 rank=3 rtt=0.000043
INFO 2026/06/10 05:51:38.011987 brd-224 DAOS[967749/0/88] rdb  src/rdb/rdb_rpc.c:364 rdb_raft_rpc_cb() 928973ff[0.1]: RPC 0 to rank 3 failed: DER_OOG(-1019): 'Out of group or member list'

[github-actions]

Ticket title is 'Destination ranks in rdb_raft_rpc_cb log messages may be incorrect'
Status is 'In Progress'
https://daosio.atlassian.net/browse/DAOS-19132