ip: drop 2-char command assumption

ip: drop 2-char command assumption

The 'ip' utility hardcodes the assumption of being a 2-char command, where
any follow-on characters are passed as an argument:

  $ ./ip-full help
  Object "-full" is unknown, try "ip help".

This confusing behaviour isn't seen with 'tc' for example, and was added in
a 2005 commit without documentation. It was noticed during testing of 'ip'
variants built/packaged with different feature sets (e.g. w/o BPF support).

Mitigate the problem by redoing the command without the 2-char assumption
if the follow-on characters fail to parse as a valid command.

Fixes: 351efcde4e62 ("Update header files to 2.6.14")
Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
Signed-off-by: David Ahern <dsahern@kernel.org>