udp: remove udp_tunnel_gro_init()

Use DEFINE_MUTEX() to initialize udp_tunnel_gro_type_lock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250707091634.311974-1-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>