examples: fix duplicated lpm6 name

examples: fix duplicated lpm6 name

When starting the ip_fragmentation or ip_reassembly example
on several sockets, it fails.

The name of the lpm6 table is the same on every socket,
resulting in a table creation failure (-EEXIST). The failure
appeared after:
commit f82f705b635d ("lpm: fix allocation of an existing object")

Indeed, before this commit the returned value when the existing
table, which was probably a bug in that case: one table for 2
sockets for lpm6, and one per socket for lpm.

Fixes: 74de12b7b63a ("examples/ip_fragmentation: overhaul")
Fixes: b84fb4cb88ff ("examples/ip_reassembly: overhaul")

Reported-by: Heng Ding <hengx.ding@intel.com>
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>