LE link_xmit_quota is not correctly allocated

LE link transmit quota should be calculated based on the total LE
buffer available and number of LE link that shares the buffer. Currently
it's been calculated based on the ACL buffer number and total physical
links(BR and LE), that cause the LE link transmit quota not being
done right.
Modify the link transmit quota allocation, and keep track of LE link
seperately, also keep track of round robin scheme for LE links
solving the problem.

Bug: 16560957
Change-Id: I70f91827b96f2c10421e91311ea34cc81a5ef4b8