iproute2: man page and /bin/ip disagree on del vs delete

iproute2: man page and /bin/ip disagree on del vs delete

Reported by Robert Henney:
> the 'ip' man page does not mention the command "del" at all but does
> claim, "As a rule, it is possible to add, delete and show (or list ) objects".
> however, 'ip' does not always recognize "delete" as a commend.
>
> robh@debian:~$ ip tunnel delete
> Command "delete" is unknown, try "ip tunnel help".

Lets use "delete" in all calls to matches() for consistency. This will
make both "del" and "delete" work everywhere.

Signed-off-by: Andreas Henriksson <andreas@fatal.se>