sss_client/common.c: fix Coverity issue
Usage of
strncpy(nssaddr.sun_path, socket_name, sizeof(nssaddr.sun_path))
1) confuses Coverity due to 3rd argument being equal to sizeof(1st)
2) again zeroes previously zeroed buffer
So replaced with strcpy()
This should be safe due to existing check of sizes.
Resolves:
https://pagure.io/SSSD/sssd/issue/3841
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>