[DCCP]: Fix for follows48

The follows48 relation identifies whether 48-bit sequence number
x is the direct successor of y. Currently, it does not handle cases
of the following type correctly:

	follows48(0x(prefix)10000LL, 0x(prefix)0FFFFLL)

where prefix is an arbitrary hex sequence of up to 7 digits.

This is fixed by reusing the new dccp_delta_seqno function.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dccp/dccp.h

@@ -144,9 +144,7 @@ static inline u64 max48(const u64 seq1, const u64 seq2)
 /* is seq1 next seqno after seq2 */
 static inline int follows48(const u64 seq1, const u64 seq2)
 {
-	int diff = (seq1 & 0xFFFF) - (seq2 & 0xFFFF);
-
-	return diff==1;
+	return dccp_delta_seqno(seq2, seq1) == 1;
 }
 
 enum {