mptcp: select CRYPTO_LIB_UTILS instead of CRYPTO

Since the only crypto functions used by the mptcp code are the SHA-256
library functions and crypto_memneq(), select only the options needed
for those: CRYPTO_LIB_SHA256 and CRYPTO_LIB_UTILS.

Previously, CRYPTO was selected instead of CRYPTO_LIB_UTILS. That does
pull in CRYPTO_LIB_UTILS as well, but it's unnecessarily broad.

Years ago, the CRYPTO_LIB_* options were visible only when CRYPTO. That
may be another reason why CRYPTO is selected here. However, that was
fixed years ago, and the libraries can now be selected directly.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Link: https://patch.msgid.link/20251204054417.491439-1-ebiggers@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>