Fix for crash when the pppos interface is restarted

[DrBomb]

Fixes #20

• Added PPPOS_CLOSING
• PPPOS_CLOSING starts polling again
• PPPOS_CLOSING still feeds UART info to stack
• Added reconnect flag to jump to PPPOS_INIT after interface is closed
• Modified disconnect state to point to PPPOS_CLOSING

[rojer]

looks good! please adjust style (braces, indent) and format with clang-format and it's good to go.

[DrBomb]

I've added the braces and did a clang-format-8. It didn't change much. I hope it was correctly applied

[DrBomb]

Added changes requested @rojer

[rojer]

ok, looks good