xfrm: export verify_userspi_info for pkfey and netlink interface

In order to check against valid IPcomp spi range, export verify_userspi_info
for both pfkey and netlink interface.

Signed-off-by: Fan Du <fan.du@windriver.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>