csp_if_udp: rx_loop: Extract socket aquisition
csp_if_udp: rx_loop: Extract socket aquisition

Extract socket() and bind() procedure to a new function
csp_if_udp_rx_get_socket().  This further help us simplify arch
dependent function, csp_if_udp_rx_loop().

Signed-off-by: Yasushi SHOJI <afa9ca3be149447780c2f7b524d61ed3d3db63f9@spacecubics.com>

libcsp/libcsp,libcsp/libcsp