carp: Widen epoch coverage
Fix panics related to calling code which expects to be running inside
the NET_EPOCH from outside that epoch.
This leads to panics (with INVARIANTS) such as this one:
panic: Assertion in_epoch(net_epoch_preempt) failed at /usr/src/sys/netinet/if_ether.c:373 cpuid = 7 time = 1586095719 KDB: stack backtrace: db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe0090819700 vpanic() at vpanic+0x182/frame 0xfffffe0090819750 panic() at panic+0x43/frame 0xfffffe00908197b0 arprequest_internal() at arprequest_internal+0x59e/frame 0xfffffe00908198c0 arp_announce_ifaddr() at arp_announce_ifaddr+0x20/frame 0xfffffe00908198e0 carp_master_down_locked() at carp_master_down_locked+0x10d/frame 0xfffffe0090819910 carp_master_down() at carp_master_down+0x79/frame 0xfffffe0090819940 softclock_call_cc() at softclock_call_cc+0x13f/frame 0xfffffe00908199f0 softclock() at softclock+0x7c/frame 0xfffffe0090819a20 ithread_loop() at ithread_loop+0x279/frame 0xfffffe0090819ab0 fork_exit() at fork_exit+0x80/frame 0xfffffe0090819af0 fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe0090819af0 --- trap 0, rip = 0, rsp = 0, rbp = 0 ---
Widen the NET_EPOCH to cover the relevant (callback / task) code.
Differential Revision: https://reviews.freebsd.org/D24302