Traditionally, the MTU in "datagram" transport mode was restricted to
2044. That is no longer the case, relax that.

In fact, choose a very large maximum and don't differenciate between
"connected" mode (they now both use now 65520). This is only the
limitation of the connection profile. Whether setting such large MTUs
actually works must be determined when activating the profile.

Initscripts "ifup-ib" from rdma-core package originally had a limit of 2044.
This was raised to 4092 in rh#1186498. It is suggested to raise it further
in bug rh#1647541.

In general, kernel often does not allow setting large MTUs. And even if it
allows it, it may not work because it also requires the entire network to
be configured accordingly. But that means, it is generally not helpful to
limit the MTU in the connection profile too strictly. Just allow large
MTUs, we need to see at activation time whether the configuration works.

Note also that a...