filter: add MOD operation

Add a new ALU opcode, to compute a modulus.

Commit ffe06c17af used an ancillary to implement XOR_X,
but here we reserve one of the available ALU opcode to implement both
MOD_X and MOD_K

Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: George Bakos <gbakos@alpinista.org>
Cc: Jay Schulist <jschlst@samba.org>
Cc: Jiri Pirko <jpirko@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/filter.h

@@ -74,6 +74,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define         BPF_LSH         0x60
 #define         BPF_RSH         0x70
 #define         BPF_NEG         0x80
+#define		BPF_MOD		0x90
+
 #define         BPF_JA          0x00
 #define         BPF_JEQ         0x10
 #define         BPF_JGT         0x20
@@ -196,6 +198,8 @@ enum {
 	BPF_S_ALU_MUL_K,
 	BPF_S_ALU_MUL_X,
 	BPF_S_ALU_DIV_X,
+	BPF_S_ALU_MOD_K,
+	BPF_S_ALU_MOD_X,
 	BPF_S_ALU_AND_K,
 	BPF_S_ALU_AND_X,
 	BPF_S_ALU_OR_K,