Add network condition for matching IP network ranges

[andrewkroh]

The network condition checks if the field is in a certain IP network range.
Both IPv4 and IPv6 addresses are supported. The network range may be specified
using CIDR notation, like "192.0.2.0/24" or "2001:db8::/32", or by using one of
these named ranges:

• loopback - Matches loopback addresses in the range of 127.0.0.0/8 or
  ::1/128.
• unicast - Matches global unicast addresses defined in RFC 1122, RFC 4632,
  and RFC 4291 with the exception of the IPv4 broadcast address
  (255.255.255.255). This includes private address ranges.
• multicast - Matches multicast addresses.
• interface_local_multicast - Matches IPv6 interface-local multicast addresses.
• link_local_unicast - Matches link-local unicast addresses.
• link_local_multicast - Matches link-local multicast addresses.
• private - Matches private address ranges defined in RFC 1918 (IPv4) and
  RFC 4193 (IPv6).
• public - Matches addresses that are not loopback, unspecified, IPv4
  broadcast, link local unicast, link local multicast, interface local
  multicast, or private.
• unspecified - Matches unspecified addresses (either the IPv4 address
  "0.0.0.0" or the IPv6 address "::").

Example

GUEST_NET: 172.16.0.0/16

processors:
  - add_fields:
      when:
        or:
          - source.ip: ${GUEST_NET}
          - destination.ip: ${GUEST_NET}
      fields:
        network.name: guest
      target: ""

[ph]

LGTM, tests are clear and show the usage, I've looked at the docs look good.