src: add specific byteorder to the struct proto_hdr_template

src: add specific byteorder to the struct proto_hdr_template

If we try to add a rule like:

nft add rule filter input udp length {55-9999}

nftable shows:

BUG: invalid byte order conversion 0 => 2
nft: src/evaluate.c:153: byteorder_conversion_op: Assertion `0' failed.

Some of the existing payload fields rely on BYTEORDER_INVALID. Therefore, if we
try to convert it in evaluation step, we hit this bug.

This patch allows to add a specific byteorder to the struct proto_hdr_template. If
we create a expression with a invalid byteorder, we will use the byteorder
added to the proto_hdr_template structure.

Signed-off-by: Alvaro Neira Ayuso <alvaroneay@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>