new remediation: require_smb_client_signing.sh

There are multiple issues:
* line 6 CLIENTSIGNINGS vs line 8's CLIENTSIGNING (IOW different variables),
* line 6 $CLIENTSIGNING - variable is referenced via $ sign & simultaneously assigned value
* the fix doesn't work (due to improper variable reference & missing quotes in the ```if [ ]``` clause):
```
[root@localhost ~]# cat /etc/redhat-release 
Red Hat Enterprise Linux Server release 6.6 (Santiago)
[root@localhost ~]# cd /root/scap-security-guide/RHEL/6/input/fixes/bash/
[root@localhost bash]# bash require_smb_client_signing.sh 
require_smb_client_signing.sh: line 6: =0: command not found
require_smb_client_signing.sh: line 8: [: -eq: unary operator expected
```