pppoe: Remove the use of cdefs

sys/cdefs.h contains the __P() macro.
The header doesn't exist in my musl toolchain,
the __P() macro has been obsoleted even by glibc,
and it's never used in the code.
This commit removes the need for this remainder.

Signed-off-by: Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

pppd/plugins/rp-pppoe/config.h

@@ -101,9 +101,6 @@
 /* Define if you have the <netpacket/packet.h> header file.  */
 #define HAVE_NETPACKET_PACKET_H 1
 
-/* Define if you have the <sys/cdefs.h> header file.  */
-#define HAVE_SYS_CDEFS_H 1
-
 /* Define if you have the <sys/dlpi.h> header file.  */
 /* #undef HAVE_SYS_DLPI_H */
 

pppd/plugins/rp-pppoe/pppoe.h

@@ -39,10 +39,6 @@
 #error Unknown method for accessing raw Ethernet frames
 #endif
 
-#ifdef HAVE_SYS_CDEFS_H
-#include <sys/cdefs.h>
-#endif
-
 #ifdef HAVE_SYS_SOCKET_H
 #include <sys/socket.h>
 #endif