net: socket: can: prepend SocketCAN data types with socketcan

Rename the SocketCAN data types to "socketcan_*" in preparation of renaming
the low-level CAN controller API data types.

This breaks the naming compatibility with the similar SocketCAN data types
from the Linux kernel, but Zephyr and Linux SocketCAN are not 100%
compatible anyways (only the structure fields are compatible, extended
functionality such filtering, error reporting etc. are not).

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>