xfrm: Fix installation of AH IPsec SAs

xfrm: Fix installation of AH IPsec SAs

[ Upstream commit a0e5ef53aac8e5049f9344857d8ec5237d31e58b ]

The SPI check introduced in ea9884b3acf3311c8a11db67bfab21773f6f82ba
was intended for IPComp SAs but actually prevented AH SAs from getting
installed (depending on the SPI).

Fixes: ea9884b3acf3 ("xfrm: check user specified spi for IPComp")
Cc: Fan Du <fan.du@windriver.com>
Signed-off-by: Tobias Brunner <tobias@strongswan.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>