A new wsrep XID format was added to keep the XID implementation
backwards compatible. Original version always reads XID seqno
part in host byte order, the new version in little endian byte
order. Wsrep XID will always be written in the new format.

Included wsrep_api.h from service_wsrep.h for wsrep type definitions.
Removed redundant wsrep XID code from mariabackup and included
service_wsrep.h in order to use