Merges HEADBANGPROTECT and EARBANGPROTECT into new secondary flag (#24881)

Unless we get a clothing item that can be worn on the head, and the
ears, and only protects from loud noises in one of the configurations,
this isn't going to be an issue.

Frees up another flag slot, all hail the secondary flags.

code/modules/mob/living/carbon/carbon_defense.dm

@@ -10,7 +10,7 @@
 	return number
 
 /mob/living/carbon/get_ear_protection()
-	if(head && (head.flags & HEADBANGPROTECT))
+	if(head && HAS_SECONDARY_FLAG(head, BANG_PROTECT))
 		return 1
 
 /mob/living/carbon/check_projectile_dismemberment(obj/item/projectile/P, def_zone)

code/modules/mob/living/carbon/human/human_defense.dm

@@ -47,7 +47,7 @@
 	return number
 
 /mob/living/carbon/human/get_ear_protection()
-	if((ears && (ears.flags & EARBANGPROTECT)) || (head && (head.flags & HEADBANGPROTECT)))
+	if((ears && HAS_SECONDARY_FLAG(ears, BANG_PROTECT)) || (head && HAS_SECONDARY_FLAG(head, BANG_PROTECT)))
 		return 1
 
 /mob/living/carbon/human/on_hit(obj/item/projectile/P)