Force unf_ext 0.0.7.4
Force unf_ext 0.0.7.4

Else it cannot compile vs arm [1][2]

[1] https://build.opnfv.org/ci/job/functest-vnf-docker-build-arm64-master/231/console
[2] https://github.com/sile/unf/pull/2/commits/74ed3e3b1ec31474cf9b8d8a90aee535607fdfe8

Change-Id: I8b0890c3b7a2a148975635c0f4eafbcc5568fc00
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

opnfv/functest,opnfv/functest