serialize: fix FromBE*() parameters
serialize: fix FromBE*() parameters

The result from DeserializeT() must be converted, not the current
buffer.  This fixes a major breakage from commit 9e00061959180

CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy