Documentation/networking: more accurate LCO explanation

In few places the term "ones-complement sum" was used but the actual
meaning is "the complement of the ones-complement sum".

Also, avoid enclosing long statements with underscore, to ease
readability.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>