net: unbreak CONFIG_RETPOLINE=n builds

The kbuild bot reported a build breakage with CONFIG_RETPOLINE=n
due to commit aaa5d90b

 ("net: use indirect call wrappers at
GRO network layer").
I screwed the wrapper implementation for such config.
Fix the issue properly ignoring the builtin symbols arguments,
when retpoline is not enabled.

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: aaa5d90b

 ("net: use indirect call wrappers at GRO network layer")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>