cmdline: fix check in port list parsing

cmdline: fix check in port list parsing

The argument ressize contains the size of the result buffer which
should be large enough to store the parsed result of a token. In
this case, it should be larger or equal to sizeof(cmdline_portlist_t)
(4 bytes), not PORTLIST_TOKEN_SIZE which is the max size of the token
string.

This is not a critical, it fixes cases where the total length of the
parsed instruction is greater than the maximum.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>