in_ioctl*: hoist identical privilege checks

[Klemens Nanni]

All cases do the same check up first, so merge it before the switch.

It could be hoisted further in both in_ioctl() and in_ioctl_change_ifaddr(),
but that meant a change in errno return semantic, so leave it for now.

Feedback? Objection OK?

Index: in.c
===================================================================
RCS file: /cvs/src/sys/netinet/in.c,v
retrieving revision 1.179
diff -u -p -r1.179 in.c
--- in.c        6 Dec 2022 22:19:39 -0000       1.179
+++ in.c        14 Apr 2023 23:05:30 -0000
@@ -283,13 +283,13 @@ in_ioctl(u_long cmd, caddr_t data, struc
                goto err;
        }
 
+       if (!privileged) {
+               error = EPERM;
+               goto err;
+       }
+
        switch (cmd) {
        case SIOCSIFDSTADDR:
-               if (!privileged) {
-                       error = EPERM;
-                       break;
-               }
-
                if ((ifp->if_flags & IFF_POINTOPOINT) == 0) {
                        error = EINVAL;
                        break;
@@ -309,11 +309,6 @@ in_ioctl(u_long cmd, caddr_t data, struc
                break;
 
        case SIOCSIFBRDADDR:
-               if (!privileged) {
-                       error = EPERM;
-                       break;
-               }
-
                if ((ifp->if_flags & IFF_BROADCAST) == 0) {
                        error = EINVAL;
                        break;
@@ -325,11 +320,6 @@ in_ioctl(u_long cmd, caddr_t data, struc
                break;
 
        case SIOCSIFNETMASK:
-               if (!privileged) {
-                       error = EPERM;
-                       break;
-               }
-
                if (ifr->ifr_addr.sa_len < 8) {
                        error = EINVAL;
                        break;
@@ -427,6 +417,9 @@ in_ioctl_change_ifaddr(u_long cmd, caddr
                        return (error);
        }
 
+       if (!privileged)
+               return (EPERM);
+
        NET_LOCK();
 
        TAILQ_FOREACH(ifa, &ifp->if_addrlist, ifa_list) {
@@ -444,11 +437,6 @@ in_ioctl_change_ifaddr(u_long cmd, caddr
        case SIOCAIFADDR: {
                int needinit = 0;
 
-               if (!privileged) {
-                       error = EPERM;
-                       break;
-               }
-
                if (ifra->ifra_mask.sin_len) {
                        if (ifra->ifra_mask.sin_len < 8) {
                                error = EINVAL;
@@ -531,11 +519,6 @@ in_ioctl_change_ifaddr(u_long cmd, caddr
                break;
            }
        case SIOCDIFADDR:
-               if (!privileged) {
-                       error = EPERM;
-                       break;
-               }
-
                if (ia == NULL) {
                        error = EADDRNOTAVAIL;
                        break;