doc: add 802.3ad modes in testpmd guide
doc: add 802.3ad modes in testpmd guide

Add testpmd commands for setting aggregators mode in mode 4 (IEEE802.3AD).

Signed-off-by: Daniel Mrzyglod <998f22cc3a6ac3535545292178d834b83a4e2a87@intel.com>
Acked-by: Jingjing Wu <64d28b617c3b4840f5ded1bfa611cba7fadfe5c7@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