MIPv6: Enhance ANI dissection

* Fix wrong length for Operator Identifier
* Display Latitude and longitude in Degrees

Bug:10712
Change-Id: Idf6ba63db3ff16710fd0de7a7fd2233148cbaf4a
Reviewed-on: https://code.wireshark.org/review/5473
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>