Raise severity of qemu entries after (PV)RDMA support has been enabled

Until the change in 1:3.1+dfsg-3, PVRDMA and RDMA support in qemu was
not enabled, so the issues affected the source package but not the
produced binary packages, and as such were classified unimportant. Since
1:3.1+dfsg-3 qemu enables rmda and pvrdma support:

>  qemu (1:3.1+dfsg-3) unstable; urgency=medium
> [...]
>    * enable rdma and pvrdma, build-depend on
>      librdmacm-dev, libibverbs-dev, libibumad-dev
> [...]