For outgoing calls send AES crypto in offer using corrected names
for keys of length 192 and 256, i.e. names containing _192_CM_
and _256_CM_ instead of _CM_192_ and CM_256_. For incoming calls
accept both naming conventions, decaying to same entry in SUITES.

+ fix after SRTP failed for 256 keys:

Tests showed loop removing '=' from keys in switch_core_media_build_crypto

 1190     if (!switch_channel_var_true(channel, "rtp_pad_srtp_keys")) {
 1191         p = strrchr((char *) b64_key, '=');
 1192
 1193         while (p && *p && *p == '=') {
 1194             *p-- = '\0';
 1195         }
 1196     }

shouldn't be executed for AES_CM_256_HMAC_SHA1_32 and AES_CM_256_HMAC_SHA1_80
keys and it is meaningless for AES_CM_128_HMAC_SHA1_32 AES_CM_128_HMAC_SHA1_80
keys. Tested calling from Bria.

Introduced switch_channel_var_false and changed this to:
	if (switch_channel_var_false(channel, "rtp_pad_srtp_keys"))
to enter the loop if var is set to false (and not if it is _not_ set).