netfilter: nf_tables: add range expression

Inverse ranges != [a,b] are not currently possible because rules are
composites of && operations, and we need to express this:

	data < a || data > b

This patch adds a new range expression. Positive ranges can be already
through two cmp expressions:

	cmp(sreg, data, >=)
	cmp(sreg, data, <=)

This new range expression provides an alternative way to express this.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>