RDMA/iwcm: Release resources if iw_cm module initialization fails

The failure during iw_cm module initialization partially left the system
with unreleased memory and other resources. Rewrite the module init/exit
routines in such way that netlink commands will be opened only after
successful initialization.

Fixes: b493d91d ("iwcm: common code for port mapper")
Link: https://lore.kernel.org/r/b01239f99cb1a3e6d2b0694c242d89e6410bcd93.1627048781.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>