infiniband: Appease Coverty
Coverity claims the call to rdma_gid2ip in cma_igmp_send overwrites addr.
Use a consistent definition of sockaddr to prevent detections and code
changes in the future.
Submitted by: firstname.lastname@example.org
Reported by: Coverity
Reviewed by: hselasky, kib
MFC after: 2 weeks
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D26229