Simplify string mangling in ifmaybeload().

- Use strlcpy() instead of strcpy().
- Use strlcat() instead of a strlcpy() with a magic number subtracted
  from the length.
- Replace strncmp(..., strlen(foo) + 1) with strcmp(...).

Differential Revision:	https://reviews.freebsd.org/D1814
Reviewed by:	rpaulo
MFC after:	2 weeks

sbin/ifconfig/ifconfig.c

@@ -1280,9 +1280,8 @@ ifmaybeload(const char *name)
 		}
 
 	/* turn interface and unit into module name */
-	strcpy(ifkind, "if_");
-	strlcpy(ifkind + MOD_PREFIX_LEN, ifname,
-	    sizeof(ifkind) - MOD_PREFIX_LEN);
+	strlcpy(ifkind, "if_", sizeof(ifkind));
+	strlcat(ifkind, ifname, sizeof(ifkind));
 
 	/* scan files in kernel */
 	mstat.version = sizeof(struct module_stat);
@@ -1299,8 +1298,8 @@ ifmaybeload(const char *name)
 				cp = mstat.name;
 			}
 			/* already loaded? */
-			if (strncmp(ifname, cp, strlen(ifname) + 1) == 0 ||
-			    strncmp(ifkind, cp, strlen(ifkind) + 1) == 0)
+			if (strcmp(ifname, cp) == 0 ||
+			    strcmp(ifkind, cp) == 0)
 				return;
 		}
 	}