doc: add limitation for l3fwd-power sample
doc: add limitation for l3fwd-power sample

L3fwd-power app needs vector mode to be disabled in order to work
properly. The app used to work previously, because it was using
Rx scalar function, but now it uses vector function.

Vector mode needs to be disabled to make the app works,
which has been documented in release notes.

Signed-off-by: Pablo de Lara <28355d9cfe41bb8148aea0fb24f47aae8f4217a1@intel.com>
Acked-by: John McNamara <af31595c36a4239b9676e9b3a777d3e2f15a6c4d@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk