cipso: adjust cached option offsets when removing CIPSO

In the Linux kernel, the following vulnerability has been resolved:

cipso: adjust cached option offsets when removing CIPSO

cipso_v4_skbuff_delattr() removes the CIPSO bytes but does not adjust
cached offsets for options that follow them.

For example, with a valid 10-byte CIPSO option followed by a seven-byte
RR option, parsing records rr at offset 30. Removing CIPSO moves RR to
offset 20, while the cached offset remains 30. Consumers such as
ip_forward_options() and __ip_options_echo() then access the wrong bytes;
the latter may interpret packet data as the option length and copy it into
fixed-size option storage.

Mirror cipso_v4_delopt() and subtract cipso_len from the srr, rr, ts and
router_alert offsets when they follow CIPSO. cipso_len is the distance
the first memmove() shifts those options. The later header move and
network-header reset relocate the bytes and their offset base together.