Adapted csma80215.cc initialize() to Ieee802154Mac.cc initialize() to solve errors from Issue #15

Here's the fix for the error described in issue #15

Original Code:
https://github.com/aarizaq/inetmanet-2.0/commit/f2b0b3a9bdb259dee5740c32de13a60522641cdc

Fix:
https://github.com/michaelkirsche/inetmanet-2.0/commit/33adcc60c8ae2b6fb85806254d4e0c40983e6647