bond: tx performance enhancement part deux

bond: tx performance enhancement part deux

- Reduce per packet cost by buffering the output packet buffer indexes in the queue and
process the queue outside the packet processing loop.
- Move unnecessary variable initialization outside of the while loop.
- There is no need to save the old interface if tracing is not enabled.

Test result for 256 bytes packet comparison. Other packet size shows similar improvement.

With the patch
--------------
BondEthernet0-output             active              52836        13526016               0          1.71e1          256.00
BondEthernet0-tx                 active              52836        13526016               0          2.68e1          256.00
TenGigabitEthernet6/0/0-output   active              52836         6762896               0          9.17e0          127.99
TenGigabitEthernet6/0/0-tx       active              52836         6762896               0          6.97e1          127.99
TenGigabitEthernet6/0/1-output   active              52836         6763120               0          9.40e0          128.00
TenGigabitEthernet6/0/1-tx       active              52836         6763120               0          7.00e1          128.00
bond-input                       active              52836        13526016               0          1.76e1          256.00

Without the patch
-----------------
BondEthernet0-output             active              60858        15579648               0          1.73e1          256.00
BondEthernet0-tx                 active              60858        15579648               0          2.94e1          256.00
TenGigabitEthernet6/0/0-output   active              60858         7789626               0          9.29e0          127.99
TenGigabitEthernet6/0/0-tx       active              60858         7789626               0          7.01e1          127.99
TenGigabitEthernet6/0/1-output   active              60858         7790022               0          9.31e0          128.00
TenGigabitEthernet6/0/1-tx       active              60858         7790022               0          7.10e1          128.00
bond-input                       active              60858        15579648               0          1.77e1          256.00

Change-Id: Ib6d73a63ceeaa2f1397ceaf4c5391c57fd865b04
Signed-off-by: Steven <sluong@cisco.com>