net: sctp: protocol.c: delete duplicated words + punctuation

Drop the repeated words "of" and "that".
Add some punctuation for readability.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: linux-sctp@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>