tftp: rework request checking to account for options

Read and write requests were not handling options.
The existing code inspecting request messages assumed that the string
before the end of the payload was the mode and that the filename
length depended on the mode length.
However the first two strings are the filename and mode which can be
followed by any number of option strings.

Rework the checking of the filename and mode to just search the first
two strings which should always exist. Any options after that are
ignored.

Absence of the filename or mode is now excludes the TFTP protocol.
Absence of the filename no longer is considered malformed packet
because it can match other protocols falsely.

0 files changed, 0 insertions, 0 deletions