BUG/MINOR: cli: fix pointer size when reporting data/transport layer name

BUG/MINOR: cli: fix pointer size when reporting data/transport layer name

In dumpstats.c we have get_conn_xprt_name() and get_conn_data_name() to
report the name of the data and transport layers used on a connection.
But when the name is not known, its pointer is reported instead. But the
static char used to report the pointer is too small as it doesn't leave
room for '0x'. Fortunately all subsystems are known so we never trigger
this case.

This fix needs to be backported to 1.6 and 1.5.