ANDROID: GKI: fix crc issue in include/net/addrconf.h

In commit 9354e0ac ("net: ipv6: support reporting otherwise unknown
prefix flags in RTM_NEWPREFIX") a union is added to fix some issues, but
that messes with the crc of a number of networking symbols for obvious
reasons.  As this does not actually change the abi at all, use some
GENKSYMS magic #define logic to preserve the crc so that all is well.

Bug: 161946584
Fixes: 9354e0ac ("net: ipv6: support reporting otherwise unknown prefix flags in RTM_NEWPREFIX")
Change-Id: I9d2df74e8f3ae60425534f1b33d50b2bc444f7f5
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>