No need for "The" here:

librdmacm relies on ARP to resolve IP address to RDMA

Use "might" to mean possibility, "may" for permission:

Without this setting, loopback connections might timeout

Typo: s/DEATCHED/DETACHED/

This is kind of backwards. Maybe:

perror("MW type must be 1 or 2");

Might also be useful for the user to show what that value actually was.