specifying keysize in bits, as it is required in IKEv2

added generic kernel SA algorithm handling, which brings us:
        aes-128, aes-256, blowfish, des, 3des and null encryption for CHILD_SAs

src/charon/config/proposal.h

@@ -112,7 +112,7 @@ struct algorithm_t {
 	u_int16_t algorithm;
 	
 	/**
-	 * the associated key size, or zero if not needed
+	 * the associated key size in bits, or zero if not needed
 	 */
 	u_int16_t key_size;
 };