doc: describe Rx bytes counter behavior for enic
doc: describe Rx bytes counter behavior for enic

Signed-off-by: Hyong Youb Kim <410cadac1eb3154f1b3752aedc2559ad69f3863e@cisco.com>
Reviewed-by: John Daley <097981eb5abe5dbeac3142a4f5a88742d916de86@cisco.com>

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