Gentoo: use slotted mbedtls

--- a/meson.build
+++ b/meson.build
@@ -49,9 +49,9 @@ if get_option('ssl').allowed()
       ssl_found = true
     endif
   else
-    mbedtls_dep = dependency('mbedtls', required: get_option('ssl'))
-    mbedtlsx509_dep = dependency('mbedx509', required: get_option('ssl'))
-    mbedtlscrypto_dep = dependency('mbedcrypto', required: get_option('ssl'))
+    mbedtls_dep = dependency('mbedtls-3', required: get_option('ssl'))
+    mbedtlsx509_dep = dependency('mbedx509-3', required: get_option('ssl'))
+    mbedtlscrypto_dep = dependency('mbedcrypto-3', required: get_option('ssl'))
     if mbedtls_dep.found() and mbedtlsx509_dep.found() and mbedtlscrypto_dep.found()
       deps += mbedtls_dep
       deps += mbedtlsx509_dep