Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index a91dc16..e5f8a71 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -704,7 +704,7 @@
 	 */
 
 	/*
-	 *	Check the other end isnt violating RFC 1122. Some routers send
+	 *	Check the other end isn't violating RFC 1122. Some routers send
 	 *	bogus responses to broadcast frames. If you see this message
 	 *	first check your netmask matches at both ends, if it does then
 	 *	get the other vendor to fix their kit.