Hello Stanislav Studený,
Having a network level bonding or having multiple interfaces for private interconnect is a personal choice and based on business requirement you can take call on the configuration. However, even if you do not choose network bonding Oracle has come up with a feature called HAIP from 11gR2 onwards, for network reduncdancy.
Ref: Grid Infrastructure Redundant Interconnect and ora.cluster_interconnect.haip (Doc ID 1210883.1)
Vandana - Oracle