build: make building with --coverage work again

build: make building with --coverage work again

When `./configure --enable-coverage` is given and lcov is present,
MISC_CFLAGS and MISC_LDFLAGS will be set to --coverage. However,

1. obexd uses per-target LDFLAGS and, in doing so, forget to re-mention
$(AM_LDFLAGS). This problem existed for a long time.

2. obexd uses per-target CFLAGS and, in doing so, forgot to re-mention
$(AM_CFLAGS). This got broken in 06dbb223fbe50acc48b3ba1d33cb424275b4baaa.

This led to no --coverage showing up in the linker line for obexd,
causing a link failure indicating unresolved symbols like
__gcov_exit.

Change-Id: I4aca476dd36f1ddc960f8f3c85cb615f9e2d36d3
Signed-off-by: himanshu <h.himanshu@samsung.com>