net: sockets: Be sure to initialize socket's queue on accept

When new socket context is created on accepting connection to a
listening socket, its recv_q FIFO should be initialized. Without
initialization, this worked by a chance when FIFO structure was
simple, but recent change to add dlist to it (which now needs
proper initialization) exposed this issue.

Jira: ZEP-2576

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>