evaluate: place byteorder conversion after numgen for IP address datatypes

evaluate: place byteorder conversion after numgen for IP address datatypes

The numgen extension generates numbers in little-endian.
This can be very tricky when trying to combine it with IP addresses, which use big endian.
This change adds a new byteorder operation to convert data type endianness.

Before this patch:
$ sudo nft -d netlink add rule nat snat_chain snat to numgen inc mod 7 offset 0x0a000001
ip nat snat_chain
  [ numgen reg 1 = inc mod 7 offset 167772161 ]
  [ nat snat ip addr_min reg 1 ]

After this patch:
$ sudo nft -d netlink add rule nat snat_chain snat to numgen inc mod 7 offset 0x0a000001
ip nat snat_chain
  [ numgen reg 1 = inc mod 7 offset 167772161 ]
  [ byteorder reg 1 = hton(reg 1, 4, 4) ]
  [ nat snat ip addr_min reg 1 ]

Regression tests have been modified to include these new cases.

Signed-off-by: Jorge Ortiz Escribano <jorge.ortiz.escribano@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>