ipv6: udp6_gro_complete() is static

net/ipv6/udp_offload.c:159:5: warning: symbol 'udp6_gro_complete' was
not declared. Should it be static?

Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 57c67ff4

 ("udp: additional GRO support")
Cc: Tom Herbert <therbert@google.com>
Acked-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>