llc: Add missing include directive for struct timeval

While including time.h is sufficient with Ubuntu's current libc6
2.19, the correct (and portable) include file is sys/time.h.

This commit modifies the include directive in llc.h accordingly.

Fixes: Jenkins #600

Addresses:
    In file included from gprs_ms.h:28,
        from gprs_ms.cpp:22:
        llc.h:68: error: field 'recv_time' has incomplete type
        llc.h:69: error: field 'expire_time' has incomplete type

Sponsored-by: On-Waves ehf
diff --git a/src/llc.h b/src/llc.h
index 887e210..fe8958f 100644
--- a/src/llc.h
+++ b/src/llc.h
@@ -24,7 +24,7 @@
 
 #include <stdint.h>
 #include <string.h>
-#include <time.h>
+#include <sys/time.h>
 
 #define LLC_MAX_LEN 1543