Update connectivity/libraries/ppp/source/ppp_service.cpp
Update connectivity/libraries/ppp/source/ppp_service.cpp

Co-authored-by: Hugues Kamba <402748a27f75fbc914c63b0503c6fbcb2aac22b4@users.noreply.github.com>
mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed,mbedmicro/mbed