panic: sleeping in an epoch section

[Yuri Pankov]

Tried updating from r353072 to r353334 and getting the following panic 
reproducibly on boot (starting dhclient?):

panic: sleeping in an epoch section
cpuid = 5
time = 1570591558
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 
0xfffffe00af780140
vpanic() at vpanic+0x19d/frame 0xfffffe00af780190
panic() at panic+0x43/frame 0xfffffe00af7801f0
_sleep() at _sleep+0x463/frame 0xfffffe00af780290
pause_sbt() at pause_sbt+0x10f/frame 0xfffffe00af7802d0
e1000_write_phy_reg_mdic() at e1000_write_phy_reg_mdic+0xee/frame 
0xfffffe00af780310
e1000_enable_phy_wakeup_reg_access_bm() at 
e1000_enable_phy_wakeup_reg_access_bm+0x2b/frame 0xfffffe00af780330
e1000_update_mc_addr_list_pch2lan() at 
e1000_update_mc_addr_list_pch2lan+0x3a/frame 0xfffffe00af780370
em_if_multi_set() at em_if_multi_set+0x1d4/frame 0xfffffe00af7803c0
iflib_if_ioctl() at iflib_if_ioctl+0x100/frame 0xfffffe00af780430
if_addmulti() at if_addmulti+0x2af/frame 0xfffffe00af7804d0
in_joingroup_locked() at in_joingroup_locked+0x235/frame 0xfffffe00af780570
in_joingroup() at in_joingroup+0x5c/frame 0xfffffe00af7805d0
in_control() at in_control+0xadf/frame 0xfffffe00af780680
ifioctl() at ifioctl+0x40f/frame 0xfffffe00af780750
kern_ioctl() at kern_ioctl+0x295/frame 0xfffffe00af7807b0
sys_ioctl() at sys_ioctl+0x15d/frame 0xfffffe00af780880
amd64_syscall() at amd64_syscall+0x2b9/frame 0xfffffe00af7809b0
fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe00af7809b0
--- syscall (54, FreeBSD ELF64, sys_ioctl), rip = 0x80048051a, rsp = 
0x7fffffffe3e8, rbp = 0x7fffffffe430 ---