nfp: Use static_assert() to check struct sizes

nfp: Use static_assert() to check struct sizes

Commit d88cabfd9abc ("nfp: Avoid -Wflex-array-member-not-at-end
warnings") introduced tagged `struct nfp_dump_tl_hdr`. We want
to ensure that when new members need to be added to the flexible
structure, they are always included within this tagged struct.

So, we use `static_assert()` to ensure that the memory layout for
both the flexible structure and the tagged struct is the same after
any changes.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/ZrVB43Hen0H5WQFP@cute
Signed-off-by: Jakub Kicinski <kuba@kernel.org>