sctp: remove the never used 'return' and redundant 'break'

In switch() had do return, and never use the 'return NULL'. The
'break' after return or goto has no effect. Remove it.

v2: make it more readable as suggested by Neil.

Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>