net: socket: mgmt: Check buf size in recvfrom()

Return EMSGSIZE if trying to copy too much data into
user supplied buffer.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
(cherry picked from commit 0a16d5c7)
(cherry picked from commit b13b4eb38a50ee02d599332eb99752e814340487)