ovn: Support multiple addresses on a single logical router port.

ovn: Support multiple addresses on a single logical router port.

Supporting multiple addresses is only mildly interesting for IPv4.
However, it is a requirement for IPv6, which will arrive in a future
commit.

This commit introduces the extract_lrp_networks() function to ovn-util.[ch].

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