net: Treat sock->sk_drops as an unsigned int when printing

Currently, procfs socket stats format sk_drops as a signed int (%d). For large
values this will cause a negative number to be printed.

We know the drop count can never be a negative so change the format specifier to
%u.

Signed-off-by: Patrick Talbert <ptalbert@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>