atm: remove dead SONET PHY ioctls

atm: remove dead SONET PHY ioctls

The SONET_* ioctls are SONET/SDH PHY controls that atm_dev_ioctl() and
the compat path only ever forwarded to the driver's ->ioctl() handler.
The PHY drivers that implemented them (the S/UNI library and the framers
on the removed PCI/SBUS adapters) are gone, and neither surviving driver
services them: solos-pci has no ->ioctl, and usbatm handles only
ATM_QUERYLOOP. They now uniformly return an error regardless.

Drop the SONET compat passthrough and the SONET cases in atm_dev_ioctl(),
along with the now-unused linux/sonet.h includes. The SONET_* uAPI
definitions are untouched.

Link: https://patch.msgid.link/20260615194416.752559-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>