[S390] use generic sockios.h header file

A compare shows that arch/s390/include/asm/sockios.h is the same as
include/asm-generic/sockios.h. This patch lets
arch/s390/include/asm/ termbits.h include the generic header.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>