res_hep_{pjsip|rtcp}: Decline module loads if res_hep had not loaded

A crash can occur in res_hep_pjsip or res_hep_rtcp if res_hep has not
loaded and does not have a configuration file. Previously when this
occurred, checks were put in to see if the configuration was loaded
successfully. While this is a good idea - and has been added to the
offending function in res_hep - the reality is res_hep_pjsip and
res_hep_rtcp have no business running if res_hep isn't also running.

As such, this patch also adds a function to res_hep that returns whether
or not it successfully loaded. Oddly enough, ast_module_check returns
"everything is peachy" even if a module declined its load - so it cannot
be solely relied on. res_hep_pjsip and res_hep_rtcp now also check this
function to see if they should continue to load; if it fails, they
decline their load as well.

ASTERISK-26096 #close

Change-Id: I007e535fcc2e51c2ca48534f48c5fc2ac38935ea

res/res_hep.exports.in

@@ -3,6 +3,7 @@
 		LINKER_SYMBOL_PREFIX*hepv3_send_packet;
 		LINKER_SYMBOL_PREFIX*hepv3_create_capture_info;
 		LINKER_SYMBOL_PREFIX*hepv3_get_uuid_type;
+		LINKER_SYMBOL_PREFIX*hepv3_is_loaded;
 	local:
 		*;
 };