utils/genrandconfig: don't build igh-ethercat drivers

igh-ethercat comes with a small number of patched Linux kernel network
drivers, which aim at replacing the ones available in upstream Linux
kernel. All those drivers are provided only for specific kernel
releases. For example:

r8169-2.6.24-ethercat.c
r8169-2.6.24-orig.c
r8169-2.6.27-ethercat.c
r8169-2.6.27-orig.c
r8169-2.6.28-ethercat.c
r8169-2.6.28-orig.c
r8169-2.6.29-ethercat.c
r8169-2.6.29-orig.c
r8169-2.6.31-ethercat.c
r8169-2.6.31-orig.c
r8169-2.6.32-ethercat.c
r8169-2.6.32-orig.c
r8169-2.6.33-ethercat.c
r8169-2.6.33-orig.c
r8169-2.6.35-ethercat.c
r8169-2.6.35-orig.c
r8169-2.6.36-ethercat.c
r8169-2.6.36-orig.c
r8169-2.6.37-ethercat.c
r8169-2.6.37-orig.c
r8169-3.10-ethercat.c
r8169-3.10-orig.c
r8169-3.12-ethercat.c
r8169-3.12-orig.c
r8169-3.14-ethercat.c
r8169-3.14-orig.c
r8169-3.16-ethercat.c
r8169-3.16-orig.c
r8169-3.2-ethercat.c
r8169-3.2-orig.c
r8169-3.4-ethercat.c
r8169-3.4-orig.c
r8169-3.6-ethercat.c
r8169-3.6-orig.c
r8169-3.8-ethercat.c
r8169-3.8-orig.c
r8169-4.4-ethercat.c
r8169-4.4-orig.c

Obviously, this doesn't play well with the random configuration
testing done by utils/genrandconfig. This commit avoids this issue by
making sure we never build any of those drivers as part of the
genrandconfig generated configurations.

Fixes:

  http://autobuild.buildroot.net/results/07b7475d780c067d99ee5618a5fd2bb024a5b4e7/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>