RPKI-RTR: enhance dissector

* fix no display all append COL_INFO... (reset by col_set_clear...)
* fix dissection when type is unknown
* fix warning about soft-deprecated (tvb_length..)
* fix indent
* fix some typo (IPV6 => IPv6...)

Ping-Bug:8296
Change-Id: I246b04098200afd1528f632cc709f631422e745b
Reviewed-on: https://code.wireshark.org/review/3888
Reviewed-by: Anders Broman <a.broman58@gmail.com>