babeld: address remaining -Wcast-qual warnings

* net.c
  * babel_send(): arguments are not treated as "const", justify
    declaration
* babel_main.c: declare constant pointers as such
diff --git a/babeld/babel_main.c b/babeld/babel_main.c
index b4d6088..1c1d0ee 100644
--- a/babeld/babel_main.c
+++ b/babeld/babel_main.c
@@ -87,14 +87,14 @@
 int wireless_hello_interval = -1;
 int wired_hello_interval = -1;
 int idle_hello_interval = -1;
-static char *pidfile = PATH_BABELD_PID;
+static const char *pidfile = PATH_BABELD_PID;
 
 const unsigned char zeroes[16] = {0};
 const unsigned char ones[16] =
     {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
      0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
 
-static char *state_file = "/var/lib/babeld/babel-state";
+static const char *state_file = "/var/lib/babeld/babel-state";
 
 unsigned char protocol_group[16]; /* babel's link-local multicast address */
 int protocol_port;                /* babel's port */
diff --git a/babeld/net.c b/babeld/net.c
index 5cb1236..eaed51d 100644
--- a/babeld/net.c
+++ b/babeld/net.c
@@ -139,16 +139,16 @@
 
 int
 babel_send(int s,
-           const void *buf1, int buflen1, const void *buf2, int buflen2,
-           const struct sockaddr *sin, int slen)
+           void *buf1, int buflen1, void *buf2, int buflen2,
+           struct sockaddr *sin, int slen)
 {
     struct iovec iovec[2];
     struct msghdr msg;
     int rc;
 
-    iovec[0].iov_base = (void*)buf1;
+    iovec[0].iov_base = buf1;
     iovec[0].iov_len = buflen1;
-    iovec[1].iov_base = (void*)buf2;
+    iovec[1].iov_base = buf2;
     iovec[1].iov_len = buflen2;
     memset(&msg, 0, sizeof(msg));
     msg.msg_name = (struct sockaddr*)sin;
diff --git a/babeld/net.h b/babeld/net.h
index e672900..4bd0f04 100644
--- a/babeld/net.h
+++ b/babeld/net.h
@@ -39,6 +39,6 @@
 int babel_socket(int port);
 int babel_recv(int s, void *buf, int buflen, struct sockaddr *sin, int slen);
 int babel_send(int s,
-               const void *buf1, int buflen1, const void *buf2, int buflen2,
-               const struct sockaddr *sin, int slen);
+               void *buf1, int buflen1, void *buf2, int buflen2,
+               struct sockaddr *sin, int slen);
 int tcp_server_socket(int port, int local);