bond: coverity woes

bond: coverity woes

coverity complains about statements in function A

function A
{
   x % vec_len (y)
}

because vec_len (y) is a macro and may return 0 if the pointer y is null.
But coverity fails to realize the same statement vec_len (y) was already
invoked and checked in the caller of function A and punt if vec_len (y) is 0.

We can fix the coverity warning and shave off a few cpu cycles by caching
the result of vec_len (y) and pass it around to avoid calling vec_len (y)
again in multiple places.

Change-Id: I095166373abd3af3859646f860ee97c52f12fb50
Signed-off-by: Steven <sluong@cisco.com>