Add some debugging macros that allow conditional output of either v4 or v6
addresses, depending on an 'af' parameter. This is done by creating a
temporary string buffer in an outer debug macro and writing addresses'
string representations into it from another macro which can only be used
when inside the outer one.
Signed-off-by: Julius Volz <juliusv@google.com>
Signed-off-by: Simon Horman <horms@verge.net.au>