net/context: Close TCP connection properly

Closing a connection, thus calling net_context_put() will not close a
TCP connection properly, and will leak tcp connection memory.

This is because: net_context_put calls net_context_unref which calls
net_tcp_unref which leads to unref tcp connection and thus sets
ctx->tcp to NULL. Back to net_context_put, that one finally calls
net_tcp_put: but that bails out directly since ctx->tcp is NULL.

Fixing it by inverting net_tcp_put() and net_context_unref() calls
within net_context_put().

Fixes #38598

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>