ss: mptcp: display seq related counters as decimal

ss: mptcp: display seq related counters as decimal

This is aligned with what is printed for TCP sockets.

The main difference here is that these counters can be larger (u32 vs
u64) but WireShark and TCPDump are also printing these MPTCP counters as
decimal and they look fine.

So it sounds better to do the same here with ss for those who want to
easily count how many bytes have been exchanged between two runs without
having to think in hexa.

Acked-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>