net: bnxt: Add TX inline buffer infrastructure

net: bnxt: Add TX inline buffer infrastructure

Add per-ring pre-allocated inline buffer fields (tx_inline_buf,
tx_inline_dma, tx_inline_size) to bnxt_tx_ring_info and helpers to
allocate and free them. A producer and consumer (tx_inline_prod,
tx_inline_cons) are added to track which slot(s) of the inline buffer
are in-use.

The inline buffer will be used by the SW USO path for pre-allocated,
pre-DMA-mapped per-segment header copies. In the future, this
could be extended to support TX copybreak.

Allocation helper is marked __maybe_unused in this commit because it
will be wired in later.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Joe Damato <joe@dama.to>
Link: https://patch.msgid.link/20260408230607.2019402-6-joe@dama.to
Signed-off-by: Jakub Kicinski <kuba@kernel.org>