Four trivial comment typo fixes of ‘ad’ to ‘as’

doc/README.plugins

@@ -253,7 +253,7 @@ This menu structure is built using the plugin_if.h interface and its
 corresponding functions.
 
 The menu items all call a callback provided by the plugin, which takes
-a pointer to the menuitem entry ad data. This pointer may be used to
+a pointer to the menuitem entry as data. This pointer may be used to
 provide userdata to each entry. The pointer must utilize WS_DLL_PUBLIC_DEF
 and has the following structure:
 

epan/dissectors/packet-ieee80211.c

@@ -27065,7 +27065,7 @@ dissect_ieee80211_common(tvbuff_t *tvb, packet_info *pinfo,
 
              otherwise, we check whether the packet starts with 0x00 0x00
              or with a copy of the sequence control field and, if so, treat
-             those two octets ad mysterious extra stuff preceding the
+             those two octets as mysterious extra stuff preceding the
              payload (possibly OLPC stuff, possibly Ruckus Wireless stuff,
              possibly Atheros stuff), and treat what follows as a frame
              using LPD;

epan/dissectors/packet-tipc.c

@@ -778,7 +778,7 @@ tipc_v1_set_col_msgtype(packet_info *pinfo, guint8 user, guint8 msg_type)
 		case TIPC_DATA_PRIO_2:
 		case TIPC_DATA_NON_REJECTABLE:
 			/*
-			 * src and dest address will be found at different location depending on User ad hdr_size
+			 * src and dest address will be found at different location depending on User as hdr_size
 			 */
 			datatype_hdr = TRUE;
 			col_append_fstr(pinfo->cinfo, COL_INFO, "%s(%u) ", val_to_str_const(msg_type, tipc_data_msg_type_values, "unknown"), msg_type);

ui/qt/main.cpp

@@ -529,7 +529,7 @@ int main(int argc, char *qt_argv[])
 
         } else {
 
-            /* select the first ad default (THIS SHOULD BE CHANGED) */
+            /* select the first as default (THIS SHOULD BE CHANGED) */
             airpcap_if_active = airpcap_get_default_if(airpcap_if_list);
         }
         break;