1. Fixing astyle and docs
2. Extra mutex lock was removed
3. Bytes are updated when send/recv > 0 and not in case of -ve error
4. Review comments
5. Guard statistics implementation in test with MBED_NW_STATS_ENABLED
SocketStats Class is added to collect and provide the statistics information.
In this phase only socket information is collected and max sockets that can
be recorded at any time are configurable through 'MBED_CONF_NSAPI_SOCKET_STATS_MAX_COUNT'
Network statistics can be enabled through a macro MBED_NW_STATS_ENABLED
More information on design is captured in #8743
Deepika