ip6_tunnel:: Correct function name parse_tvl_tnl_enc_lim() in the kerneldoc comments

Fix the following W=1 kernel build warning(s):

 net/ipv6/ip6_tunnel.c:401: warning: expecting prototype for parse_tvl_tnl_enc_lim(). Prototype was for ip6_tnl_parse_tlv_enc_lim() instead

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>