Fork: import latest net-snmp from openwrt packages with agentx

This is the stock version of net-snmp from openwrt-trunk-packages, plus
the agentx/tcp patches suggested:
http://patchwork.openwrt.org/patch/5118/
net-snmp: No need to patch documentation that won't be installed

This must have been imported blindly from debian's packaging, but is
just noise for an openwrt build.