Pin neutron to the last Rocky version

Pin neutron to the last Rocky version

networking sfc and bgpvpn depend on it.
If unpinned, neutron 14.0.0.0b2 is selected and raise side effects [1]

neutron 14.0.0.0b2 has requirement neutron-lib>=1.24.0, but you'll have neutron-lib 1.18.0 which is incompatible.
neutron 14.0.0.0b2 has requirement pyroute2>=0.5.3; sys_platform != "win32", but you'll have pyroute2 0.5.2 which is incompatible.

[1] https://build.opnfv.org/ci/job/functest-features-docker-build-amd64-hunter/125/console

Change-Id: Id4ff5e67b62e9162bd3e7d866ef57fb1012cd994
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>