tests: net: socket: af_packet: Switch to blocking sockets with timeout

Packet socket tests used non-blocking sockets so in results the test
code was overly complicated with delays and loops scattered all across
the test code, making it difficult to read.
As packet sockets do support blocking operation with timeout,
reconfigure the sockets to use that and simplify the test code by
getting rid of unnecessary loops and delays.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>