vnet/interface: vnet_(put|get)frame_to_sw_interface is not worker thread aware

vnet/interface: vnet_(put|get)frame_to_sw_interface is not worker thread aware

When heavy traffic is running using worker threads, it may crash here

DBGvpp# 0: /home/sluong/vpp3/vpp/build-data/../src/vlib/main.c:1128 (dispatch_pending_node) assertion `f->flags & VLIB_FRAME_PENDING' fails

Thread 1 "vpp_main" received signal SIGABRT, Aborted.
0x00007ffff5d50428 in __GI_raise (sig=sig@entry=6)
    at ../sysdeps/unix/sysv/linux/raise.c:54
54	../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb)

No crash was observed if only main thread was used.

Change-Id: I96f8b02ec23accc85c0f1ddecfeff6043b5e3c2b
Signed-off-by: Steven <sluong@cisco.com>