util: fromString: Reduce string allocations

Change-Id: Ie6f7fa5dcc958081e7d7e2b880c17fe3548955a7
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/util.hpp b/src/util.hpp
index b1d27c4..804d492 100644
--- a/src/util.hpp
+++ b/src/util.hpp
@@ -44,7 +44,11 @@
  *  @returns A mac address in network byte order
  *  @throws std::runtime_error for bad mac
  */
-ether_addr fromString(std::string_view str);
+ether_addr fromString(const char* str);
+inline ether_addr fromString(const std::string& str)
+{
+    return fromString(str.c_str());
+}
 
 /** @brief Converts the given mac address bytes into a string
  *  @param[in] mac - The mac address