ovn.at: Fix MSYS IPv6 interpretation

ovn.at: Fix MSYS IPv6 interpretation

Unfortunately MSYS transforms `0::` into the location of the binaries i.e.:
c:\MinGW\msys\1.0\64.

Currently the test:
`testing ovn -- IPv6 Neighbor Solicitation for unknown MAC`
fails because of the above:
"ovn-nbctl: lrp0_ip6: invalid network address: aef0;c:\MinGW\msys\1.0\64"

This patch uses the full form of the IPv6 address instead of its shorter
notation.

Signed-off-by: Alin Gabriel Serdean <aserdean@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>