Modified Netmask::FromBits for longer prefixes.

Do not try handle prefixes longer than 32 bits.
Updated testsuite for Netmask.

Test Netmask::FromBits for prefixes longer than 32bits.
Updated default CanonicalizeIP output for IPv6 input. bnc837517

When CanonicalizeIP is invoked with IPv6 input it returns empty NETMASK.
NETMASKs are not used in IPv6 world that much. Moreover Netmask::FromBits
usesi IPv4 specific implementation.
Updated testsuite. Extended IPv6 testdata for CanonicalizeIP.

Used prefix longer than 32 which has nonzero modulo when divided by 8.
Updated changelog.