In the (corner) case that someone requests to install a shared edge IRQ
while the related support is not enabled (!CONFIG_XENO_OPT_SHIRQ_EDGE),
BUT the opposite type (CONFIG_XENO_OPT_SHIRQ_LEVEL), Xenomai so far
incorrectly installs the level-type handler. For the other way around,
the non-shared dispatch handler is installed, which is also not correct.

This patch fixes the issue by returning an error on registration,
clearly indicating the system misconfiguration to the caller.

Jan