Revise times of polling mgmt port link status to 100

The polling loop of checking link status is a total 5 seconds in the
worst case. It may be timeout eventually if the link partner has
capibility of 1000 full duplex.

We ran test of booting on Accton AS5710_54x repeatedly and found the
polling loop has probability over 50 times. The test result are:

- 40 times (55%)
- 50 times (45%)
- 69 times (8%)
- 79 times (2%)