package/clamav: bump version to 0.98.7, enable ipv6 support

Clamav uses AC_TRY_RUN in m4/reorganization/code_checks/ipv6.m4 to check
for ipv6 support, which is not cross-compile safe. Since buildroot
supports ipv6 out-of-the-box now this patch forces ipv6 support.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>