WI-84821 SNMP2 and SNMP3 stubs $host param should be $hostname

[StefNieuwhuis]

WI-84821 SNMP2 and SNMP3 stubs $host param should be $hostname

Changed $host paramter to $hostname in all snmp2 and snmp3 functions to be consistent with the actual extension.

[LolGleb]

Thanks for the PR. A couple of asks before this can land:

1. Drop the PhpStormStubsMap.php changes please. The proposed map is missing valid mappings;
2. Fix snmp2_real_walk docblock. Line 601 still says @param string $host while the signature on line 619 was renamed to $hostname;
3. (Optional) Would you mind covering the snmp1 family too? snmpgetnext, snmprealwalk, and snmpset still use $host in both signature and docblock, and php.net documents them as $hostname. Otherwise the file is left half-converted.