[bug: #223] patches/buildroot: fix memory leak in netsnmp (IP-MIB)

After IP-MIB has been enabled, WRS was runnig out of memory after 1-2 months.
SNMP was leaking about 10MB/month of memory. A leak was observed no matter if
and which OIDs were queried.
Signed-off-by: Adam Wujek <dev_public@wujek.eu>