l2: coverity complains dead codes

l2: coverity complains dead codes

Coverity complains dead codes in 2 places due to a recent commit as
pointed out in Fixes. The dead codes are
      if (seed < L2_BD_ID_MAX % 2)
        is_seed_low = 1;
and
      if (is_seed_low)
        seed += (2 * (i % 2) - 1) * i;

seed can never be less than (L2_BD_ID_MAX % 2).
Consequently, is_seed_low is always 0.

There is also other problem. The inner loop is iterating only once.

The fix is to greatly simplify the code to generate a random bd_id.

Type: fix
Fixes: Ieb6919f958f437fc603d5e1f48cab01de780951d

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: I318773b9a59950920e051548ef14e36054ebd5e6