Use ip_parse() and ipv6_parse() and variants in more places.

Use ip_parse() and ipv6_parse() and variants in more places.

This saves some code and improves clarity, in my opinion.

Some of these changes just change an inet_pton() call into a similar
ip_parse() or ipv6_parse() call.  In those cases the benefit is better
type safety, since inet_pton()'s output parameter is type "void *".

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>