NSAPI: Use IPv6 conversion routines from frameworks
NSAPI: Use IPv6 conversion routines from frameworks

Share IPv6 conversion code with mbed_trace, Nanostack and
mbed client.

Output formatting is better, being conformant to RFC 5952.

c1728p9/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,c1728p9/mbed-os,andcor02/mbed-os,betzw/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,betzw/mbed-os,betzw/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,betzw/mbed-os,kjbracey-arm/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,andcor02/mbed-os,betzw/mbed-os,c1728p9/mbed-os,mbedmicro/mbed,mbedmicro/mbed,andcor02/mbed-os,betzw/mbed-os,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed