ROA revalidation: updated documentation

ROA_VALID if there is a matching ROA, or ROA_INVALID if there are some relevant

ROAs but none of them match. There is also an extended variant

<cf>roa_check(<m/table/, <m/prefix/, <m/asn/)</cf>, which allows to specify a

prefix and an ASN as arguments.

prefix and an ASN as arguments. It shall be explicitly noted that if the content

of the target table changes, the whole half-channel (import or export) reloads

completely.

<sect>Control structures

<label id="control-structures">

<p>The RPKI-RTR protocol receives and maintains a set of ROAs from a cache

server (also called validator). You can validate routes (RFC 6483) using

function <cf/roa_check()/ in filter and set it as import filter at the BGP

protocol. BIRD should re-validate all of affected routes after RPKI update by

RFC 6811, but we don't support it yet! You can use a BIRD's client command

<cf>reload in <m/bgp_protocol_name/</cf> for manual call of revalidation of all

routes.

protocol. BIRD re-validates all the affected routes after RPKI update by

RFC 6811 by reloading whole the affected half-channel.

<sect1>Supported transports

<p>