[PATCH] Fix build warning: Implicit declaration nxsem_post()

[Nathan Hartman]

Recently this warning started showing up in builds:

icmp/icmp_netpoll.c: In function 'icmp_poll_eventhandler':
icmp/icmp_netpoll.c:129:11: warning: implicit declaration of function
'nxsem_post'; did you mean 'sem_post'?
[-Wimplicit-function-declaration]
           nxsem_post(info->fds->sem);
           ^~~~~~~~~~
           sem_post

Caused by removal of include of nuttx/kmalloc.h, which includes
nuttx/userspace.h, which includes pthread.h, which includes sched.h,
which includes semaphore.h.

In other words, icmp/icmp_netpoll.c should include semaphore.h directly.

Patch attached.

Thanks,
Nathan