When delivering an ICMP packet to the ctlinput function, ensure that

When delivering an ICMP packet to the ctlinput function, ensure that
the outer IP header, the ICMP header, the inner IP header and the
first n bytes are stored in contgous memory. The ctlinput functions
currently rely on this for n = 8. This fixes a bug in case the inner IP
header had options.
While there, remove the options from the outer header and provide a
way to increase n to allow improved ICMP handling for SCTP. This will
be added in another commit.

MFC after:	1 week