[NETFILTER]: nf_conntrack_sctp: basic cleanups

Reindent switch cases properly, get rid of weird constructs like "!(x == y)",
put logical operations on the end of the line instead of the next line, get
rid of superfluous braces.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>