MPR redundancy

As explained in section 4.5, MPR redundancy specifies how many MPRs should at best cover every 2-hop neighbor. The redundancy parameter can be set in the configuration file, it defaults to 1.

The MPR calculation algorithms were modified to add redundancy in the calculation. While two hop neighbors used to have a boolean value covered, stating if the node was covered by a MPR, they now have a integer variable that is updated with the number of MPRs covering the node during calculation. MPR calculation becomes a rather complex algorithm when considering that the calculation must respect willingness, including always adding nodes with willingness WILL_ALWAYS and never adding nodes with willingness WILL_NEVER, redundancy and optimization of the calculated MPR set as described in section 8.3.1 of RFC3626 . The MPR calculation algorithms are located in the src/mpr.c file.