devtools: skip removed DLB driver in ABI check

devtools: skip removed DLB driver in ABI check

The eventdev driver DLB was removed in DPDK 21.05,
breaking the ABI check.
The exception was agreed so we just need to skip this check.

Note: complete removal of a driver cannot be ignored
in devtools/libabigail.abignore, so the script must be patched.

Fixes: 698fa829415d ("event/dlb: remove driver")

Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: David Marchand <david.marchand@redhat.com>