[SCTP]: Replace char msg[] with static const char[].

133886    2004     220  136110   213ae sctp.new/sctp.o
134018    2004     220  136242   21432 sctp.old/sctp.o

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>