Fix argv leaks in add_route() and add_route_ipv6()

Fix argv leaks in add_route() and add_route_ipv6()

If a route structure is passed to add_route() or add_route_ipv6()
without the RT_DEFINED flag set, both functions leak an "argv"
structure allocation.

Add appropriate argv_free() calls.

Backport to 2.4: argv_free() was called argv_reset() back then.

Signed-off-by: David Korczynski <david@adalogics.com>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20210714162533.10098-1-david@adalogics.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22637.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit a11bea18b1c93b260352ec505db15be0ec9431ee)