net: mpls: make function ipgre_mpls_encap_hlen static

The function ipgre_mpls_encap_hlen is local to the source and
does not need to be in global scope, so make it static.

Cleans up sparse warning:
symbol 'ipgre_mpls_encap_hlen' was not declared. Should it be static?

Fixes: bdc47641 ("ip_tunnel: add mpls over gre support")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/mpls/af_mpls.c

@@ -41,7 +41,7 @@ static int label_limit = (1 << 20) - 1;
 static int ttl_max = 255;
 
 #if IS_ENABLED(CONFIG_NET_IP_TUNNEL)
-size_t ipgre_mpls_encap_hlen(struct ip_tunnel_encap *e)
+static size_t ipgre_mpls_encap_hlen(struct ip_tunnel_encap *e)
 {
 	return sizeof(struct mpls_shim_hdr);
 }