more NET_LOCK in pppx

[Jonathan Matthew]

Reading through if_pppx.c I spotted a couple of places we need NET_LOCK().

ok?

Index: if_pppx.c
===================================================================
RCS file: /cvs/src/sys/net/if_pppx.c,v
retrieving revision 1.63
diff -u -p -u -p -r1.63 if_pppx.c
--- if_pppx.c   12 Aug 2017 20:27:28 -0000      1.63
+++ if_pppx.c   27 Mar 2018 23:56:56 -0000
@@ -392,6 +392,8 @@ pppxwrite(dev_t dev, struct uio *uio, in
        proto = ntohl(*(uint32_t *)(th + 1));
        m_adj(top, sizeof(uint32_t));
 
+       NET_LOCK();
+
        switch (proto) {
        case AF_INET:
                ipv4_input(&pxi->pxi_if, top);
@@ -403,9 +405,12 @@ pppxwrite(dev_t dev, struct uio *uio, in
 #endif
        default:
                m_freem(top);
-               return (EAFNOSUPPORT);
+               error = EAFNOSUPPORT;
+               break;
        }
 
+       NET_UNLOCK();
+
        return (error);
 }
 
@@ -583,8 +588,10 @@ pppxclose(dev_t dev, int flags, int mode
        pxd = pppx_dev_lookup(dev);
 
        /* XXX */
+       NET_LOCK();
        while ((pxi = LIST_FIRST(&pxd->pxd_pxis)))
                pppx_if_destroy(pxd, pxi);
+       NET_UNLOCK();
 
        LIST_REMOVE(pxd, pxd_entry);