dpdk: fix extended stat strings

- These were displaying blank, apparently dpdk extended stat strings
must be within the heap so they are identified as vectors by
format_c_identifier even though they are not.

Type: fix
Change-Id: I2b153b100203b9856ce3af6d5ecb2daae410fb5b
Signed-off-by: Christian Hopps <chopps@labn.net>