netxen_nic: Replace fake flex-array with flexible-array member

Zero-length arrays as fake flexible arrays are deprecated and we are
moving towards adopting C99 flexible-array members instead.

Transform zero-length array into flexible-array member in struct
nx_cardrsp_rx_ctx_t.

Address the following warnings found with GCC-13 and
-fstrict-flex-arrays=3 enabled:
drivers/net/ethernet/qlogic/netxen/netxen_nic_ctx.c:361:26: warning: array subscript <unknown> is outside array bounds of ‘char[0]’ [-Warray-bounds=]
drivers/net/ethernet/qlogic/netxen/netxen_nic_ctx.c:372:25: warning: array subscript <unknown> is outside array bounds of ‘char[0]’ [-Warray-bounds=]

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/21
Link: https://github.com/KSPP/linux/issues/265
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html

 [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/ZAZ57I6WdQEwWh7v@work


Signed-off-by: Jakub Kicinski <kuba@kernel.org>