Smalls improvements

Smalls improvements

- Improve robustness reading a BCM socket
  Adding checks on system calls and remove the initialization of the
  struct that will hold the received message, not so much needed in
  that case.
- More accurate log message at subscription/unsubscription step whether
  this is a FD CAN messages or not and if this a subscription or an
  unsubscription that is requested.
- Initialize the full struct of vehicle message to avoid memory warning
  about conditionnal jump based on uninitialized bytes.
- Memleak: Free raw pointer on active diagnostic requests

Change-Id: I4bbf4d851c0fa1efdb6fa6034fac3d1dcafa1a73
Signed-off-by: Romain Forlot <romain.forlot@iot.bzh>