netlink_delinearize: handle relational and lookup concat expressions

netlink_delinearize: handle relational and lookup concat expressions

When the RHS length differs from the LHS length (which is only the
first expression), both expressions are assumed to be concat expressions.

The LHS concat expression is reconstructed from the available register
values, advancing by the number of registers required by the subexpressions'
register space, until the RHS length has been reached.

The RHS concat expression is reconstructed by splitting the data value
into multiple subexpressions based on the LHS concat expressions types.

Signed-off-by: Patrick McHardy <kaber@trash.net>