* Accept all RFC4486 bgp error subcodes

Bio-BGP used to only decode AdministrativeShut and AdministrativeReset
error subcodes when error code "Cease" was sent by a BGP peer. Other BGP
packets could not be decoded. With this commit Bio-BGP accepts and
decodes all error codes defined in RFC4486.

* Set OtherConfigChange to value defined in RFC4486