slirp: Read current time only once per if_start call

No need to update the current time for each packet we send from the
queue. Processing time is comparably short.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>

slirp/if.c

@@ -157,9 +157,8 @@ diddit:
 void
 if_start(Slirp *slirp)
 {
+    uint64_t now = qemu_get_clock_ns(rt_clock);
     int requeued = 0;
-    uint64_t now;
-
 	struct mbuf *ifm, *ifqt;
 
 	DEBUG_CALL("if_start");
@@ -172,8 +171,6 @@ if_start(Slirp *slirp)
         if (!slirp_can_output(slirp->opaque))
             return;
 
-        now = qemu_get_clock_ns(rt_clock);
-
 	/*
 	 * See which queue to get next packet from
 	 * If there's something in the fastq, select it immediately