TCP bonding in socklnd over-complicates the code and there is no evidence it's being used anywhere. With LNet Multi-Rail, the use_tcp_bonding option has become obsolete. Add a deprecation message for earlier releases. Remove it in the 2.15 release.
Multi-Rail feature doesn't need to be explicitly enabled. To use MR instead of the use_tcp_bonding configuration option, group the interfaces on the same network using the lnetctl utility:
or via the /etc/modprobe.d/lnet.conf or /etc/modprobe.d/lustre.conf configuration file:
and make sure dynamic discovery is enabled:
MR will aggregate the throughput of all available networks/interfaces shared between peer nodes.