net-snmp: avoid duplicate section names

net-snmp: avoid duplicate section names

It seems that UCI can't handle duplicate section names in a single
config file, even if they use different types. After the previous
commit, running `uci export` results in the following error:

uci: Parse error (section of different type overwrites prior section with same name) at line 17, byte 23

Append a 6 to the com2sec6 section names to solve this.

Fixes: 0e1c8b4ccc2c ("net-snmp: snmpd: listen on IPv6 by default")
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>