[Bridge + 8021q] Store interface data in shared memory

* defined if_data and vlan_data structures in switch.h and
functions to get, set and delete them;
* on if_add we create an if_data structure in shared memory;
this will be deleted on if_remove;
* moved shared memory specific structures in switch.h;

Signed-off-by: Claudiu Ghioc <claudiu.ghioc@gmail.com>