Define and use macros for route addition status code

Define and use macros for route addition status code

- Instead of 0, 1, 2 use RTA_ERROR, RTA_SUCCESS, RTA_EEXIST
  as the return code of route addition functions.

- Also fix a logging error: status -> (status == RTA_SUCCESS)

v2: fold long lines
    use "bool ret = .." pattern for android too
    fix two more lines where status was directly assigned to bool

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230115164818.1973210-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26041.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 328cc40c8368a9e1f9abc92eb4d34687470e3a92)