Revert "bgpd: Handle Addpath capability using dynamic capabilities"

Revert "bgpd: Handle Addpath capability using dynamic capabilities"

This reverts commit 05cf9d03b345393b8d63ffe9345c42debd8362b6.

TL;DR; Handling BGP AddPath capability is not trivial (possible) dynamically.

When the sender is AddPath-capable and sends NLRIs encoded with AddPath ID,
and at the same time the receiver sends AddPath capability "disable-addpath-rx"
(flag update) via dynamic capabilities, both peers are out of sync about the
AddPath state. The receiver thinks already he's not AddPath-capable anymore,
hence it tries to parse NLRIs as non-AddPath, while they are actually encoded
as AddPath.

AddPath capability itself does not provide (in RFC) any mechanism on backward
compatible way to handle NLRIs if they come mixed (AddPath + non-AddPath).

This explains why we have failures in our CI periodically.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>