The libnfs v3v4 autopkgtest currently tests NFSv4.0 behavior. In
particular, the NFSv4 part of the test uses the NFSv4.0 SETCLIENTID flow.

With nfs-utils 2.9.1, NFSv4.0 is disabled by default. Because of that, the
test can fail with NFS4ERR_MINOR_VERS_MISMATCH unless NFSv4.0 is explicitly
enabled in the test setup.

The attached patch updates debian/tests/v3v4 to enable NFSv4.0 before
starting nfs-kernel-server, so the test setup matches what the test is
trying to exercise.