net-snmp-5.5 patch for sysObjectID watch fix

When you get the sysObjectID from net-snmp-5.5 it will return only 1.3 instead of the whole enterprise OID. This is because in agent/mibgroup/mibII/system_mib.c the sysObjectIDLength is in oid units instead of sizeof units. This patch adds a sysObjectID_sizeof variable and updates it to sysObjectIDLength * sizeof(oid) when setting default during startup and when sysObjectID is set in a config file.