OFI transport: inject_size capped at 16 bytes due to fi_getinfo hint

[bcmIntc]

Description

shmem_transport_ofi_max_buffered_send was initialized to sizeof(long double)
(16 bytes) before being passed as tx_attr.inject_size in the fi_getinfo
hints. The CXI provider treats the hint value as a ceiling rather than a floor,
returning exactly 16 — even though CXI's natural inject_size is 192 bytes.

As a result, any put in the 17-192 byte range was sent via RDMA (with MR
registration lookup) rather than the faster inline inject path.

Root cause

src/transport_ofi.c, function query_for_fabric:

shmem_transport_ofi_max_buffered_send = sizeof(long double);  // hint = 16
...
tx_attr.inject_size = shmem_transport_ofi_max_buffered_send;
...
ret = fi_getinfo(..., &hints, &info);
...
shmem_transport_ofi_max_buffered_send = info->tx_attr->inject_size;  // adopts 16, not 192

Fix

Initialize shmem_transport_ofi_max_buffered_send = 0 (no minimum requirement)
so the provider returns its natural inject_size, which is then adopted. This works for all providers except VERBS,
which will provide a conservative injection size.

See: #1231

Impact

Puts in the 17-192 byte range now use the inline inject path on CXI. Operations
outside that range (AMOs ≤ 16 bytes, large puts > 192 bytes) are unaffected.