src/apps: Fix speling issues

Found by codespell

src/apps/altcp_tls/altcp_tls_mbedtls.c

@@ -48,7 +48,7 @@
  *   GOOD custom entropy
  *
  * Missing things / @todo:
- * - some unhandled/untested things migh be caught by LWIP_ASSERTs...
+ * - some unhandled/untested things might be caught by LWIP_ASSERTs...
  */
 
 #include "lwip/opt.h"

src/apps/mdns/mdns.c

@@ -1792,7 +1792,7 @@ mdns_probe_conflict(struct netif *netif, s8_t slot)
 }
 
 /**
- * Loockup matching request for response MDNS packet
+ * Lookup matching request for response MDNS packet
  */
 #if LWIP_MDNS_SEARCH
 static struct mdns_request *

src/apps/mqtt/mqtt.c

@@ -318,7 +318,7 @@ mqtt_append_request(struct mqtt_request_t **tail, struct mqtt_request_t *r)
 
   LWIP_ASSERT("mqtt_append_request: tail != NULL", tail != NULL);
 
-  /* Iterate trough queue to find head, and count total timeout time */
+  /* Iterate through queue to find head, and count total timeout time */
   for (iter = *tail; iter != NULL; iter = iter->next) {
     time_before += iter->timeout_diff;
     head = iter;

src/apps/netbiosns/netbiosns.c

@@ -391,7 +391,7 @@ netbiosns_recv(void *arg, struct udp_pcb *upcb, struct pbuf *p, const ip_addr_t
               resp->resp_hdr.authorityRRs  = 0;
               resp->resp_hdr.additionalRRs = 0;
 
-              /* prepare NetBIOS header datas */
+              /* prepare NetBIOS header data */
               MEMCPY( resp->resp_name.encname, netbios_question_hdr->encname, sizeof(netbios_question_hdr->encname));
               resp->resp_name.nametype     = netbios_question_hdr->nametype;
               resp->resp_name.type         = netbios_question_hdr->type;

src/apps/smtp/smtp.c

@@ -1305,7 +1305,7 @@ smtp_process(void *arg, struct altcp_pcb *pcb, struct pbuf *p)
     LWIP_DEBUGF(SMTP_DEBUG_TRACE, ("smtp_process: received response code: %d\n", response_code));
     if (smtp_is_response_finished(s) != ERR_OK) {
       LWIP_DEBUGF(SMTP_DEBUG_TRACE, ("smtp_process: partly received response code: %d\n", response_code));
-      /* wait for next packet to complete the respone */
+      /* wait for next packet to complete the response */
       return;
     }
   } else {

src/apps/snmp/snmp_core.c

@@ -584,7 +584,7 @@ snmp_oid_prefix(struct snmp_obj_id *target, const u32_t *oid, u8_t oid_len)
 
 /**
  * Combine two OIDs into struct snmp_obj_id
- * @param target Assignmet target
+ * @param target Assignment target
  * @param oid1 OID 1
  * @param oid1_len OID 1 length
  * @param oid2 OID 2