[IPSEC]: Do xfrm_state_check_space before encapsulation

While merging the IPsec output path I moved the encapsulation output
operation to the top of the loop so that it sits outside of the locked
section.  Unfortunately in doing so it now sits in front of the space
check as well which could be a fatal error.

This patch rearranges the calls so that the space check happens as
the thing on the output path.

This patch also fixes an incorrect goto should the encapsulation output
fail.

Thanks to Kazunori MIYAZAWA for finding this bug.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>