These ioctl(2)s are handled by ifioctl() and never passed down to the drivers.
ok? Index: net/if_gre.c =================================================================== RCS file: /cvs/src/sys/net/if_gre.c,v retrieving revision 1.87 diff -u -p -r1.87 if_gre.c --- net/if_gre.c 11 Aug 2017 21:24:19 -0000 1.87 +++ net/if_gre.c 18 Oct 2017 12:36:35 -0000 @@ -456,12 +456,6 @@ gre_ioctl(struct ifnet *ifp, u_long cmd, } ifp->if_mtu = ifr->ifr_mtu; break; - case SIOCGIFMTU: - ifr->ifr_mtu = sc->sc_if.if_mtu; - break; - case SIOCGIFHARDMTU: - ifr->ifr_hardmtu = sc->sc_if.if_hardmtu; - break; case SIOCADDMULTI: case SIOCDELMULTI: break; Index: net/if_spppsubr.c =================================================================== RCS file: /cvs/src/sys/net/if_spppsubr.c,v retrieving revision 1.172 diff -u -p -r1.172 if_spppsubr.c --- net/if_spppsubr.c 15 Aug 2017 06:08:52 -0000 1.172 +++ net/if_spppsubr.c 18 Oct 2017 12:36:32 -0000 @@ -864,12 +864,6 @@ sppp_ioctl(struct ifnet *ifp, u_long cmd } ifp->if_mtu = ifr->ifr_mtu; break; - case SIOCGIFMTU: - ifr->ifr_mtu = ifp->if_mtu; - break; - case SIOCGIFHARDMTU: - ifr->ifr_hardmtu = ifp->if_hardmtu; - break; case SIOCADDMULTI: case SIOCDELMULTI: break; Index: dev/usb/if_umb.c =================================================================== RCS file: /cvs/src/sys/dev/usb/if_umb.c,v retrieving revision 1.15 diff -u -p -r1.15 if_umb.c --- dev/usb/if_umb.c 11 Aug 2017 21:24:19 -0000 1.15 +++ dev/usb/if_umb.c 18 Oct 2017 12:36:42 -0000 @@ -734,12 +734,6 @@ umb_ioctl(struct ifnet *ifp, u_long cmd, } ifp->if_mtu = ifr->ifr_mtu; break; - case SIOCGIFMTU: - ifr->ifr_mtu = ifp->if_mtu; - break; - case SIOCGIFHARDMTU: - ifr->ifr_hardmtu = ifp->if_hardmtu; - break; case SIOCSIFADDR: case SIOCAIFADDR: case SIOCSIFDSTADDR: