NLM: Remove unused argument from svc_addsock() function

Clean up: The svc_addsock() function no longer uses its "proto"
argument, so remove it.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>