Log Message:
Upgrade net-snmp to version 5.7.2.1.

Upstream changes:
   * 5.{5,6,7}.2.1 *
       snmpd:
         - SECURITY: a denial of service attack vector was discovered on
           the linux implementation of the ICMP-MIB.  This release fixes
           this bug and all users are encouraged to update their SNMP
           agent if they make use of the ICMP-MIB table objects.

Fixes CVE-2014-2284.