ANDROID: CRC ABI fixups in ip.h and ipv6.h

In commit 6e933443 ("net: use struct_group to copy ip/ipv6 header
addresses"), struct_group() is added to some structures to resolve a
build warning.  This changes the CRC of a number of networking
functions, without changing any actual structure sizes or interactions.
To resolve this, use __GENKSYMS__ #ifdef hack to preserve the Android
kernel CRC abi.

Bug: 161946584
Fixes: 6e933443 ("net: use struct_group to copy ip/ipv6 header addresses")
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ia70eb3aa41316fbced713c99c85ddaeccec2ffec