Fix WiFiStation buffer management

[pennam]

The issue raised trying to download a file with WiFi interface. Download stops before reaching the end of the file.

The root cause of the problem is that each time getStationRx is called the package is poped from the queue and if the subsequentially pbuf_alloc call fails the package is lost.

With the proposed changes we first check the size of the package in the queue calling peekStationRxMsgSize() and we pop it only if pbuf_alloc call is succesful, otherwise we retry the next run.

edit - Issue and proposed solution description

/cc @andreagilardoni

[Fashion-Corp]

What was the problem? I also see that a variable, if_num, seem to be undefined, yet it is being called by reference in CnetIf.cpp, line 1376:

uint8_t if_num;

The outcome is not in use, however, that could change :-) Well. Let me know what is the problem with the WiFIStation buffer management, and what the bugfix does.

[pennam]

Sketch to reproduce the issue:

DownloadC33-PR.zip

[pennam]

What was the problem? I also see that a variable, if_num, seem to be undefined, yet it is being called by reference in CnetIf.cpp, line 1376:

uint8_t if_num;

The outcome is not in use, however, that could change :-) Well. Let me know what is the problem with the WiFIStation buffer management, and what the bugfix does.

@Fashion-Corp i've updated the PR description with an explanation of the problem. if_num is initialized here if a valid mesage is found, however it is not used in CWifiStation::task() so it should not be an issue.