tun: Fix compiler warnings

tun: Fix compiler warnings

Fixes two compiler warnings identified by using CFLAGS=-O2

1) ifconfig_ipv6_remote is only used on Solaris, move the
   declaration and assignment of this variable into the
   TARGET_SOLARIS block.

2) Linux have it's own open_tun() function and does not
   depend on open_tun_generic() at all.  So exclude
   open_tun_generic() if TARGET_LINUX is defined.

v2 - Move changes from 1) into the proper if() block
     directly
   - Fix up incorrect comment tags related to changes in 2)

v3 - Minor coding style adjustments and change WIN32 to _WIN32

Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1479165185-11730-1-git-send-email-davids@openvpn.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg13063.html