avr32: wire up accept4 syscall

The accept4 syscall is missing on AVR32.  Fix this.
Signed-off-by: Mans Rullgard <mans@mansr.com>
Acked-by: Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>

arch/avr32/include/uapi/asm/unistd.h

@@ -333,5 +333,6 @@
 #define __NR_memfd_create	318
 #define __NR_bpf		319
 #define __NR_execveat		320
+#define __NR_accept4		321
 
 #endif /* _UAPI__ASM_AVR32_UNISTD_H */

arch/avr32/kernel/syscall_table.S

@@ -334,4 +334,5 @@ sys_call_table:
 	.long	sys_memfd_create
 	.long	sys_bpf
 	.long	sys_execveat		/* 320 */
+	.long	sys_accept4
 	.long	sys_ni_syscall		/* r8 is saturated at nr_syscalls */