ipv6: sr: add missing seg6_local_exit

ipv6: sr: add missing seg6_local_exit

Currently, we only call seg6_local_exit() in seg6_init() if
seg6_local_init() failed. But forgot to call it in seg6_exit().

Fixes: d1df6fd8a1d2 ("ipv6: sr: define core operations for seg6local lightweight tunnel")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240509131812.1662197-2-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>