Add alternative for supporting snmp during scans

[jjnicola]

What:
Add alternative nasl function to perform snmp scan, spawning a new process and using the binary snmpget

** Why **
In case libsnmp is not present, but the binary, still have support for snmp scans

How:
running this nasl script with openvas-nasl against a target with a running snmp agent is a way to test the new functions. To test
the functions, be sure you don't have the libsnmp-dev installed or remove the add_definition of "HAVE_NETSNMP" in nasl/CMakeLists.txt.

openvas-nasl -X -d -D -i <path-to-script> snmp_test.nasl -t <ip-with-running-and_configured-snmp-server>

include("misc_func.inc");
include("dump.inc");


oid = '.1.3.6.1.2.1.1.1.0';

## uncomment this line to test the error handling
#oid = '.1.3.6.1.2.1.1.1.0.3.3.3.3';
protocol = 'udp';
port = 161;
community = 'public';

display("version 1");
ret = snmpv1_get( port:port, oid:oid, protocol:protocol, community:community );
display (ret, "\n");

display("version 2c");
ret = snmpv2c_get( port:port, oid:oid, protocol:protocol, community:community );
display (ret, "\n");

user = "some user";
pass = "password_ultra_xxl";

display("version 3");
ret = snmpv3_get(port:port, protocol:"udp", username:user, oid:oid,
                  authpass:pass, authproto:"md5", privpass:pass,
                  privproto:"des");

display (ret, "\n");

Checklist:

• Tests
• CHANGELOG Entry

[ArnoStiefvater]

Suggested change

	We assume that if there is no erros, we have an output.
	We assume a valid output if there are no errors.

[ArnoStiefvater]

Function documentation missing.

[ArnoStiefvater]

Function documentation missing.