[Coverity CID :208406] Macro compares unsigned to 0 in subsys/net/l2/ppp/ppp_l2.c

[zephyrbot]

Static code scan issues found in file:

https://github.com/zephyrproject-rtos/zephyr/tree/93b78b7bf8bfad75196de969a7487f95f235aad3/subsys/net/l2/ppp/ppp_l2.c#L346

Category: Integer handling issues
Function: echo_reply_handler
Component: Networking
CID: 208406

Details:

340     static void echo_reply_handler(void *user_data, size_t user_data_len)
341     {
342         struct ppp_context *ctx = user_data;
343         u32_t end_time = k_cycle_get_32();
344         int time_diff;
345    
>>>     CID 208406:  Integer handling issues  (NO_EFFECT)
>>>     This less-than-zero comparison of an unsigned value is never true. "end_time - ctx->shell.echo_req_data < 0U".
346         time_diff = abs(end_time - ctx->shell.echo_req_data);
347         ctx->shell.echo_req_data =
348             k_cyc_to_ns_floor64(time_diff) / 1000;
349    
350         k_sem_give(&ctx->shell.wait_echo_reply);
351     }

Please fix or provide comments in coverity using the link:

https://scan9.coverity.com/reports.htm#v32951/p12996.

Note: This issue was created automatically. Priority was set based on classification
of the file affected and the impact field in coverity. Assignees were set using the CODEOWNERS file.