sctp: fix warning when compiling without IPv6

net/sctp/protocol.c: In function ‘sctp_addr_wq_timeout_handler’:
net/sctp/protocol.c:676: warning: label ‘free_next’ defined but not used

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>