cmdline: fix dynamic tokens initialization

cmdline: fix dynamic tokens initialization

To avoid redundant calls to the token-generating function and provide it
with helpful context, a temporary fixed-size array allocated on the stack
of cmdline_parse() and cmdline_complete() keeps the address of preceding
tokens for the command instance being processed (cmdline_parse_inst_t).

Like the static tokens array in cmdline_parse_inst_t, it must be
NULL-terminated, however this is not properly enforced as it is initialized
once at the beginning of each function and a NULL terminator is never
appended once replaced with generated tokens.

When several commands rely on dynamic tokens, subsequent ones inherit an
already initialized array whose tokens are not regenerated, which causes
various issues such as mixed and repeated tokens from the first command.

Enforcing NULL termination of the dynamic tokens array and reinitializing
its first entry at each iteration solves these issues. Doing so is also
less expensive than a full memset() at each iteration.

Fixes: 4fffc05a2b2c ("cmdline: support dynamic tokens")
Cc: stable@dpdk.org
Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>