Changelog:

1. The 802.11 model in GTNetS did not backoff after a single re-try. The longRetry count was incremented in GTNetS only if there was an ACK timeout. 
It was not incremented if the node fails to gain access of the medium. Now the long retry count is incremented to keep track of the number of times 
the packet is failed to be transmitted and the node goes into backoff procedure till a maximum number for retry count is reached.

- R